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	$42.70	13.791%	$48.5888	$48.59	$48.60	$48.60
Purchase #2	$199.37	13.254%	$225.7945	$225.79	$225.80	$225.80
Purchase #3	$142.28	8.126%	$153.8417	$153.84	$153.85	$153.80
Purchase #4	$201.57	11.724%	$225.2021	$225.20	$225.20	$225.20
Purchase #5	$36.37	11.103%	$40.4082	$40.41	$40.40	$40.40
Purchase #6	$28.67	13.317%	$32.488	$32.49	$32.50	$32.50
Purchase #7	$183.52	9.123%	$200.2625	$200.26	$200.25	$200.30
7 purchase totals =	$834.48		$926.5858	$926.58	$926.60	$926.60