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	$55.45	13.287%	$62.8176	$62.82	$62.80	$62.80
Purchase #2	$205.60	11.770%	$229.7991	$229.80	$229.80	$229.80
Purchase #3	$192.94	8.258%	$208.873	$208.87	$208.85	$208.90
Purchase #4	$130.70	12.171%	$146.6075	$146.61	$146.60	$146.60
Purchase #5	$65.90	8.668%	$71.6122	$71.61	$71.60	$71.60
Purchase #6	$58.48	4.860%	$61.3221	$61.32	$61.30	$61.30
Purchase #7	$24.78	8.589%	$26.9084	$26.91	$26.90	$26.90
7 purchase totals =	$733.85		$807.9399	$807.94	$807.85	$807.90