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	$59.50	11.630%	$66.4199	$66.42	$66.40	$66.40
Purchase #2	$141.38	8.261%	$153.0594	$153.06	$153.05	$153.10
Purchase #3	$59.28	3.870%	$61.5741	$61.57	$61.55	$61.60
Purchase #4	$180.35	9.672%	$197.7935	$197.79	$197.80	$197.80
Purchase #5	$204.93	11.219%	$227.9211	$227.92	$227.90	$227.90
Purchase #6	$43.43	9.700%	$47.6427	$47.64	$47.65	$47.60
Purchase #7	$78.75	4.802%	$82.5316	$82.53	$82.55	$82.50
7 purchase totals =	$767.62		$836.9423	$836.93	$836.90	$836.90