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	$99.61	5.267%	$104.8565	$104.86	$104.85	$104.90
Purchase #2	$203.45	6.462%	$216.5969	$216.60	$216.60	$216.60
Purchase #3	$88.61	13.784%	$100.824	$100.82	$100.80	$100.80
Purchase #4	$137.33	10.341%	$151.5313	$151.53	$151.55	$151.50
Purchase #5	$140.86	13.863%	$160.3874	$160.39	$160.40	$160.40
Purchase #6	$133.40	13.584%	$151.5211	$151.52	$151.50	$151.50
Purchase #7	$226.40	11.796%	$253.1061	$253.11	$253.10	$253.10
7 purchase totals =	$1,029.66		$1,138.8233	$1,138.83	$1,138.80	$1,138.80