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	$139.25	6.409%	$148.1745	$148.17	$148.15	$148.20
Purchase #2	$151.89	4.768%	$159.1321	$159.13	$159.15	$159.10
Purchase #3	$93.88	10.598%	$103.8294	$103.83	$103.85	$103.80
Purchase #4	$122.99	7.253%	$131.9105	$131.91	$131.90	$131.90
Purchase #5	$55.96	11.377%	$62.3266	$62.33	$62.35	$62.30
Purchase #6	$250.55	3.186%	$258.5325	$258.53	$258.55	$258.50
Purchase #7	$12.42	7.820%	$13.3912	$13.39	$13.40	$13.40
7 purchase totals =	$826.94		$877.2968	$877.29	$877.35	$877.20