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	$80.54	11.552%	$89.844	$89.84	$89.85	$89.80
Purchase #2	$66.66	6.305%	$70.8629	$70.86	$70.85	$70.90
Purchase #3	$203.54	3.238%	$210.1306	$210.13	$210.15	$210.10
Purchase #4	$140.47	6.447%	$149.5261	$149.53	$149.55	$149.50
Purchase #5	$25.29	11.552%	$28.2115	$28.21	$28.20	$28.20
Purchase #6	$60.43	9.521%	$66.1835	$66.18	$66.20	$66.20
Purchase #7	$53.72	6.705%	$57.3219	$57.32	$57.30	$57.30
7 purchase totals =	$630.65		$672.0805	$672.07	$672.10	$672.00