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	$71.79	12.214%	$80.5584	$80.56	$80.55	$80.60
Purchase #2	$34.47	9.426%	$37.7191	$37.72	$37.70	$37.70
Purchase #3	$96.27	6.516%	$102.543	$102.54	$102.55	$102.50
Purchase #4	$84.58	4.609%	$88.4783	$88.48	$88.50	$88.50
Purchase #5	$139.57	11.385%	$155.46	$155.46	$155.45	$155.50
Purchase #6	$237.28	10.599%	$262.4293	$262.43	$262.45	$262.40
Purchase #7	$9.61	13.755%	$10.9319	$10.93	$10.95	$10.90
7 purchase totals =	$673.57		$738.1200	$738.12	$738.15	$738.10