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	$156.73	8.680%	$170.3342	$170.33	$170.35	$170.30
Purchase #2	$249.58	11.700%	$278.7809	$278.78	$278.80	$278.80
Purchase #3	$135.28	12.224%	$151.8166	$151.82	$151.80	$151.80
Purchase #4	$121.88	3.193%	$125.7716	$125.77	$125.75	$125.80
Purchase #5	$99.60	12.281%	$111.8319	$111.83	$111.85	$111.80
Purchase #6	$89.65	13.166%	$101.4533	$101.45	$101.45	$101.50
Purchase #7	$204.89	13.421%	$232.3883	$232.39	$232.40	$232.40
7 purchase totals =	$1,057.61		$1,172.3768	$1,172.37	$1,172.40	$1,172.40