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	$232.29	5.262%	$244.5131	$244.51	$244.50	$244.50
Purchase #2	$35.73	7.308%	$38.3411	$38.34	$38.35	$38.30
Purchase #3	$171.70	10.512%	$189.7491	$189.75	$189.75	$189.70
Purchase #4	$130.32	5.772%	$137.8421	$137.84	$137.85	$137.80
Purchase #5	$42.36	6.636%	$45.171	$45.17	$45.15	$45.20
Purchase #6	$137.97	9.647%	$151.28	$151.28	$151.30	$151.30
Purchase #7	$36.65	9.525%	$40.1409	$40.14	$40.15	$40.10
7 purchase totals =	$787.02		$847.0373	$847.03	$847.05	$846.90