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	$70.43	11.544%	$78.5604	$78.56	$78.55	$78.60
Purchase #2	$66.28	9.257%	$72.4155	$72.42	$72.40	$72.40
Purchase #3	$114.67	8.343%	$124.2369	$124.24	$124.25	$124.20
Purchase #4	$77.95	11.817%	$87.1614	$87.16	$87.15	$87.20
Purchase #5	$75.27	7.220%	$80.7045	$80.70	$80.70	$80.70
Purchase #6	$48.55	3.528%	$50.2628	$50.26	$50.25	$50.30
Purchase #7	$180.39	8.857%	$196.3671	$196.37	$196.35	$196.40
7 purchase totals =	$633.54		$689.7086	$689.71	$689.65	$689.80