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	$134.76	8.460%	$146.1607	$146.16	$146.15	$146.20
Purchase #2	$107.81	3.780%	$111.8852	$111.89	$111.90	$111.90
Purchase #3	$237.28	12.165%	$266.1451	$266.15	$266.15	$266.10
Purchase #4	$74.63	13.140%	$84.4364	$84.44	$84.45	$84.40
Purchase #5	$91.57	13.464%	$103.899	$103.90	$103.90	$103.90
Purchase #6	$14.45	9.805%	$15.8668	$15.87	$15.85	$15.90
Purchase #7	$164.70	6.145%	$174.8208	$174.82	$174.80	$174.80
7 purchase totals =	$825.20		$903.2140	$903.23	$903.20	$903.20