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	$144.37	3.552%	$149.498	$149.50	$149.50	$149.50
Purchase #2	$116.40	11.750%	$130.077	$130.08	$130.10	$130.10
Purchase #3	$99.82	11.307%	$111.1066	$111.11	$111.10	$111.10
Purchase #4	$17.40	4.582%	$18.1973	$18.20	$18.20	$18.20
Purchase #5	$238.89	6.142%	$253.5626	$253.56	$253.55	$253.60
Purchase #6	$32.25	12.687%	$36.3416	$36.34	$36.35	$36.30
Purchase #7	$141.40	7.720%	$152.3161	$152.32	$152.30	$152.30
7 purchase totals =	$790.53		$851.0992	$851.11	$851.10	$851.10