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	$99.76	5.559%	$105.3057	$105.31	$105.30	$105.30
Purchase #2	$123.33	9.226%	$134.7084	$134.71	$134.70	$134.70
Purchase #3	$202.95	9.651%	$222.5367	$222.54	$222.55	$222.50
Purchase #4	$238.40	5.385%	$251.2378	$251.24	$251.25	$251.20
Purchase #5	$61.76	12.286%	$69.3478	$69.35	$69.35	$69.30
Purchase #6	$201.81	12.553%	$227.1432	$227.14	$227.15	$227.10
Purchase #7	$223.54	13.764%	$254.308	$254.31	$254.30	$254.30
7 purchase totals =	$1,151.55		$1,264.5876	$1,264.60	$1,264.60	$1,264.40