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	$30.76	5.730%	$32.5225	$32.52	$32.50	$32.50
Purchase #2	$218.33	11.331%	$243.069	$243.07	$243.05	$243.10
Purchase #3	$235.42	4.686%	$246.4518	$246.45	$246.45	$246.50
Purchase #4	$206.30	7.530%	$221.8344	$221.83	$221.85	$221.80
Purchase #5	$182.97	9.188%	$199.7813	$199.78	$199.80	$199.80
Purchase #6	$89.87	10.827%	$99.6002	$99.60	$99.60	$99.60
Purchase #7	$105.84	7.274%	$113.5388	$113.54	$113.55	$113.50
7 purchase totals =	$1,069.49		$1,156.7980	$1,156.79	$1,156.80	$1,156.80