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	$216.38	12.542%	$243.5184	$243.52	$243.50	$243.50
Purchase #2	$115.79	9.594%	$126.8989	$126.90	$126.90	$126.90
Purchase #3	$118.34	7.675%	$127.4226	$127.42	$127.40	$127.40
Purchase #4	$22.78	7.393%	$24.4641	$24.46	$24.45	$24.50
Purchase #5	$50.84	9.628%	$55.7349	$55.73	$55.75	$55.70
Purchase #6	$240.64	12.698%	$271.1965	$271.20	$271.20	$271.20
Purchase #7	$33.73	4.626%	$35.2903	$35.29	$35.30	$35.30
7 purchase totals =	$798.50		$884.5257	$884.52	$884.50	$884.50