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	$52.51	7.121%	$56.2492	$56.25	$56.25	$56.20
Purchase #2	$158.78	7.434%	$170.5837	$170.58	$170.60	$170.60
Purchase #3	$88.80	12.235%	$99.6647	$99.66	$99.65	$99.70
Purchase #4	$62.44	13.215%	$70.6914	$70.69	$70.70	$70.70
Purchase #5	$191.73	9.789%	$210.4984	$210.50	$210.50	$210.50
Purchase #6	$63.99	13.352%	$72.5339	$72.53	$72.55	$72.50
Purchase #7	$173.47	9.470%	$189.8976	$189.90	$189.90	$189.90
7 purchase totals =	$791.72		$870.1189	$870.11	$870.15	$870.10