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	$247.65	13.131%	$280.1689	$280.17	$280.15	$280.20
Purchase #2	$227.82	13.349%	$258.2317	$258.23	$258.25	$258.20
Purchase #3	$221.81	11.630%	$247.6065	$247.61	$247.60	$247.60
Purchase #4	$143.59	5.764%	$151.8665	$151.87	$151.85	$151.90
Purchase #5	$248.41	13.776%	$282.631	$282.63	$282.65	$282.60
Purchase #6	$77.36	7.747%	$83.3531	$83.35	$83.35	$83.40
Purchase #7	$169.96	8.568%	$184.5222	$184.52	$184.50	$184.50
7 purchase totals =	$1,336.60		$1,488.3799	$1,488.38	$1,488.35	$1,488.40