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	$172.58	13.753%	$196.3149	$196.31	$196.30	$196.30
Purchase #2	$97.42	13.208%	$110.2872	$110.29	$110.30	$110.30
Purchase #3	$106.35	7.731%	$114.5719	$114.57	$114.55	$114.60
Purchase #4	$151.28	13.830%	$172.202	$172.20	$172.20	$172.20
Purchase #5	$126.47	13.706%	$143.804	$143.80	$143.80	$143.80
Purchase #6	$90.44	10.240%	$99.7011	$99.70	$99.70	$99.70
Purchase #7	$98.79	6.221%	$104.9357	$104.94	$104.95	$104.90
7 purchase totals =	$843.33		$941.8168	$941.81	$941.80	$941.80