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	$61.70	4.402%	$64.416	$64.42	$64.40	$64.40
Purchase #2	$98.67	13.242%	$111.7359	$111.74	$111.75	$111.70
Purchase #3	$17.92	10.844%	$19.8632	$19.86	$19.85	$19.90
Purchase #4	$67.54	10.550%	$74.6655	$74.67	$74.65	$74.70
Purchase #5	$233.74	13.360%	$264.9677	$264.97	$264.95	$265.00
Purchase #6	$49.36	11.138%	$54.8577	$54.86	$54.85	$54.90
Purchase #7	$51.72	11.236%	$57.5313	$57.53	$57.55	$57.50
7 purchase totals =	$580.65		$648.0373	$648.05	$648.00	$648.10