Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$38.84	5.647%	$41.0333	$41.03	$41.05	$41.00
Purchase #2	$44.90	3.136%	$46.3081	$46.31	$46.30	$46.30
Purchase #3	$98.30	3.320%	$101.5636	$101.56	$101.55	$101.60
Purchase #4	$90.70	6.857%	$96.9193	$96.92	$96.90	$96.90
Purchase #5	$175.71	5.660%	$185.6552	$185.66	$185.65	$185.70
Purchase #6	$233.77	9.416%	$255.7818	$255.78	$255.80	$255.80
Purchase #7	$181.31	6.171%	$192.4986	$192.50	$192.50	$192.50
7 purchase totals =	$863.53		$919.7599	$919.76	$919.75	$919.80