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	$94.35	6.563%	$100.5422	$100.54	$100.55	$100.50
Purchase #2	$41.52	6.190%	$44.0901	$44.09	$44.10	$44.10
Purchase #3	$68.59	10.696%	$75.9264	$75.93	$75.95	$75.90
Purchase #4	$85.44	6.450%	$90.9509	$90.95	$90.95	$91.00
Purchase #5	$215.89	10.483%	$238.5217	$238.52	$238.50	$238.50
Purchase #6	$61.89	13.300%	$70.1214	$70.12	$70.10	$70.10
Purchase #7	$56.79	11.331%	$63.2249	$63.22	$63.20	$63.20
7 purchase totals =	$624.47		$683.3776	$683.37	$683.35	$683.30