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	$193.32	6.496%	$205.8781	$205.88	$205.90	$205.90
Purchase #2	$153.88	10.811%	$170.516	$170.52	$170.50	$170.50
Purchase #3	$72.59	7.725%	$78.1976	$78.20	$78.20	$78.20
Purchase #4	$175.74	13.385%	$199.2628	$199.26	$199.25	$199.30
Purchase #5	$87.68	5.855%	$92.8137	$92.81	$92.80	$92.80
Purchase #6	$155.91	6.707%	$166.3669	$166.37	$166.35	$166.40
Purchase #7	$56.59	13.681%	$64.3321	$64.33	$64.35	$64.30
7 purchase totals =	$895.71		$977.3672	$977.37	$977.35	$977.40