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	$238.72	13.327%	$270.5342	$270.53	$270.55	$270.50
Purchase #2	$136.78	8.200%	$147.996	$148.00	$148.00	$148.00
Purchase #3	$178.91	11.482%	$199.4524	$199.45	$199.45	$199.50
Purchase #4	$130.52	8.487%	$141.5972	$141.60	$141.60	$141.60
Purchase #5	$65.55	7.859%	$70.7016	$70.70	$70.70	$70.70
Purchase #6	$17.31	12.159%	$19.4147	$19.41	$19.40	$19.40
Purchase #7	$166.78	11.155%	$185.3843	$185.38	$185.40	$185.40
7 purchase totals =	$934.57		$1,035.0804	$1,035.07	$1,035.10	$1,035.10