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	$133.70	13.267%	$151.438	$151.44	$151.45	$151.40
Purchase #2	$110.30	12.273%	$123.8371	$123.84	$123.85	$123.80
Purchase #3	$230.41	11.336%	$256.5293	$256.53	$256.55	$256.50
Purchase #4	$87.56	3.452%	$90.5826	$90.58	$90.60	$90.60
Purchase #5	$245.31	6.329%	$260.8357	$260.84	$260.85	$260.80
Purchase #6	$184.90	13.425%	$209.7228	$209.72	$209.70	$209.70
Purchase #7	$45.73	6.871%	$48.8721	$48.87	$48.85	$48.90
7 purchase totals =	$1,037.91		$1,141.8176	$1,141.82	$1,141.85	$1,141.70