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	$134.91	11.414%	$150.3086	$150.31	$150.30	$150.30
Purchase #2	$138.76	5.552%	$146.464	$146.46	$146.45	$146.50
Purchase #3	$193.73	11.368%	$215.7532	$215.75	$215.75	$215.80
Purchase #4	$71.39	9.352%	$78.0664	$78.07	$78.05	$78.10
Purchase #5	$166.33	5.434%	$175.3684	$175.37	$175.35	$175.40
Purchase #6	$36.99	3.664%	$38.3453	$38.35	$38.35	$38.30
Purchase #7	$113.43	9.564%	$124.2784	$124.28	$124.30	$124.30
7 purchase totals =	$855.54		$928.5843	$928.59	$928.55	$928.70