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	$112.90	7.857%	$121.7706	$121.77	$121.75	$121.80
Purchase #2	$229.32	5.768%	$242.5472	$242.55	$242.55	$242.50
Purchase #3	$124.58	12.518%	$140.1749	$140.17	$140.15	$140.20
Purchase #4	$175.37	3.115%	$180.8328	$180.83	$180.85	$180.80
Purchase #5	$214.85	13.282%	$243.3864	$243.39	$243.40	$243.40
Purchase #6	$147.32	5.491%	$155.4093	$155.41	$155.40	$155.40
Purchase #7	$41.71	12.410%	$46.8862	$46.89	$46.90	$46.90
7 purchase totals =	$1,046.05		$1,131.0074	$1,131.01	$1,131.00	$1,131.00