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	$250.33	4.700%	$262.0955	$262.10	$262.10	$262.10
Purchase #2	$132.69	10.462%	$146.572	$146.57	$146.55	$146.60
Purchase #3	$186.38	11.656%	$208.1045	$208.10	$208.10	$208.10
Purchase #4	$154.47	13.715%	$175.6556	$175.66	$175.65	$175.70
Purchase #5	$61.58	6.530%	$65.6012	$65.60	$65.60	$65.60
Purchase #6	$122.98	7.278%	$131.9305	$131.93	$131.95	$131.90
Purchase #7	$87.46	4.299%	$91.2199	$91.22	$91.20	$91.20
7 purchase totals =	$995.89		$1,081.1792	$1,081.18	$1,081.15	$1,081.20