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	$204.35	12.372%	$229.6322	$229.63	$229.65	$229.60
Purchase #2	$199.31	4.671%	$208.6198	$208.62	$208.60	$208.60
Purchase #3	$143.38	11.240%	$159.4959	$159.50	$159.50	$159.50
Purchase #4	$126.50	11.353%	$140.8615	$140.86	$140.85	$140.90
Purchase #5	$108.42	13.373%	$122.919	$122.92	$122.90	$122.90
Purchase #6	$53.60	11.283%	$59.6477	$59.65	$59.65	$59.60
Purchase #7	$85.65	10.610%	$94.7375	$94.74	$94.75	$94.70
7 purchase totals =	$921.21		$1,015.9136	$1,015.92	$1,015.90	$1,015.80