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	$148.74	13.104%	$168.2309	$168.23	$168.25	$168.20
Purchase #2	$49.38	5.657%	$52.1734	$52.17	$52.15	$52.20
Purchase #3	$37.34	8.800%	$40.6259	$40.63	$40.65	$40.60
Purchase #4	$50.31	6.584%	$53.6224	$53.62	$53.60	$53.60
Purchase #5	$125.92	12.259%	$141.3565	$141.36	$141.35	$141.40
Purchase #6	$150.61	7.523%	$161.9404	$161.94	$161.95	$161.90
Purchase #7	$146.72	12.721%	$165.3843	$165.38	$165.40	$165.40
7 purchase totals =	$709.02		$783.3338	$783.33	$783.35	$783.30