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	$87.74	13.218%	$99.3375	$99.34	$99.35	$99.30
Purchase #2	$71.53	3.712%	$74.1852	$74.19	$74.20	$74.20
Purchase #3	$22.61	6.449%	$24.0681	$24.07	$24.05	$24.10
Purchase #4	$90.57	11.228%	$100.7392	$100.74	$100.75	$100.70
Purchase #5	$130.41	8.533%	$141.5379	$141.54	$141.55	$141.50
Purchase #6	$168.32	4.301%	$175.5594	$175.56	$175.55	$175.60
Purchase #7	$126.75	10.856%	$140.51	$140.51	$140.50	$140.50
7 purchase totals =	$697.93		$755.9373	$755.95	$755.95	$755.90