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	$108.71	13.493%	$123.3782	$123.38	$123.40	$123.40
Purchase #2	$171.56	9.220%	$187.3778	$187.38	$187.40	$187.40
Purchase #3	$232.93	6.130%	$247.2086	$247.21	$247.20	$247.20
Purchase #4	$26.30	9.799%	$28.8771	$28.88	$28.90	$28.90
Purchase #5	$166.52	8.572%	$180.7941	$180.79	$180.80	$180.80
Purchase #6	$248.48	5.636%	$262.4843	$262.48	$262.50	$262.50
Purchase #7	$83.96	11.149%	$93.3207	$93.32	$93.30	$93.30
7 purchase totals =	$1,038.46		$1,123.4408	$1,123.44	$1,123.50	$1,123.50