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	$155.70	5.401%	$164.1094	$164.11	$164.10	$164.10
Purchase #2	$53.72	6.845%	$57.3971	$57.40	$57.40	$57.40
Purchase #3	$131.28	7.220%	$140.7584	$140.76	$140.75	$140.80
Purchase #4	$93.43	11.265%	$103.9549	$103.95	$103.95	$104.00
Purchase #5	$159.92	11.676%	$178.5923	$178.59	$178.60	$178.60
Purchase #6	$151.66	5.140%	$159.4553	$159.46	$159.45	$159.50
Purchase #7	$150.75	4.715%	$157.8579	$157.86	$157.85	$157.90
7 purchase totals =	$896.46		$962.1253	$962.13	$962.10	$962.30