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	$34.25	4.855%	$35.9128	$35.91	$35.90	$35.90
Purchase #2	$243.76	11.754%	$272.4116	$272.41	$272.40	$272.40
Purchase #3	$152.96	10.833%	$169.5302	$169.53	$169.55	$169.50
Purchase #4	$229.34	6.641%	$244.5705	$244.57	$244.55	$244.60
Purchase #5	$79.39	10.606%	$87.8101	$87.81	$87.80	$87.80
Purchase #6	$127.72	7.341%	$137.0959	$137.10	$137.10	$137.10
Purchase #7	$228.75	10.708%	$253.2446	$253.24	$253.25	$253.20
7 purchase totals =	$1,096.17		$1,200.5757	$1,200.57	$1,200.55	$1,200.50