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	$37.54	13.142%	$42.4735	$42.47	$42.45	$42.50
Purchase #2	$106.68	13.807%	$121.4093	$121.41	$121.40	$121.40
Purchase #3	$105.90	11.860%	$118.4597	$118.46	$118.45	$118.50
Purchase #4	$85.80	8.808%	$93.3573	$93.36	$93.35	$93.40
Purchase #5	$35.84	6.670%	$38.2305	$38.23	$38.25	$38.20
Purchase #6	$67.61	6.639%	$72.0986	$72.10	$72.10	$72.10
Purchase #7	$18.50	11.379%	$20.6051	$20.61	$20.60	$20.60
7 purchase totals =	$457.87		$506.6340	$506.64	$506.60	$506.70