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	$237.35	9.467%	$259.8199	$259.82	$259.80	$259.80
Purchase #2	$223.79	6.494%	$238.3229	$238.32	$238.30	$238.30
Purchase #3	$149.82	5.653%	$158.2893	$158.29	$158.30	$158.30
Purchase #4	$156.61	6.588%	$166.9275	$166.93	$166.95	$166.90
Purchase #5	$200.82	13.361%	$227.6516	$227.65	$227.65	$227.70
Purchase #6	$202.79	3.642%	$210.1756	$210.18	$210.20	$210.20
Purchase #7	$83.54	6.707%	$89.143	$89.14	$89.15	$89.10
7 purchase totals =	$1,254.72		$1,350.3298	$1,350.33	$1,350.35	$1,350.30