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	$72.67	7.792%	$78.3324	$78.33	$78.35	$78.30
Purchase #2	$191.48	12.123%	$214.6931	$214.69	$214.70	$214.70
Purchase #3	$103.72	5.629%	$109.5584	$109.56	$109.55	$109.60
Purchase #4	$131.79	4.658%	$137.9288	$137.93	$137.95	$137.90
Purchase #5	$69.37	3.161%	$71.5628	$71.56	$71.55	$71.60
Purchase #6	$236.90	5.583%	$250.1261	$250.13	$250.15	$250.10
Purchase #7	$20.70	6.563%	$22.0585	$22.06	$22.05	$22.10
7 purchase totals =	$826.63		$884.2601	$884.26	$884.30	$884.30