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	$248.50	12.318%	$279.1102	$279.11	$279.10	$279.10
Purchase #2	$33.78	9.856%	$37.1094	$37.11	$37.10	$37.10
Purchase #3	$125.28	5.503%	$132.1742	$132.17	$132.15	$132.20
Purchase #4	$93.27	9.425%	$102.0607	$102.06	$102.05	$102.10
Purchase #5	$111.87	10.417%	$123.5235	$123.52	$123.50	$123.50
Purchase #6	$155.65	8.323%	$168.6047	$168.60	$168.60	$168.60
Purchase #7	$136.43	10.604%	$150.897	$150.90	$150.90	$150.90
7 purchase totals =	$904.78		$993.4797	$993.47	$993.40	$993.50