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	$123.91	7.743%	$133.5044	$133.50	$133.50	$133.50
Purchase #2	$97.33	8.116%	$105.2293	$105.23	$105.25	$105.20
Purchase #3	$156.53	12.193%	$175.6157	$175.62	$175.60	$175.60
Purchase #4	$104.38	10.323%	$115.1551	$115.16	$115.15	$115.20
Purchase #5	$126.25	4.174%	$131.5197	$131.52	$131.50	$131.50
Purchase #6	$149.35	10.677%	$165.2961	$165.30	$165.30	$165.30
Purchase #7	$21.81	3.656%	$22.6074	$22.61	$22.60	$22.60
7 purchase totals =	$779.56		$848.9277	$848.94	$848.90	$848.90