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	$110.92	7.542%	$119.2856	$119.29	$119.30	$119.30
Purchase #2	$238.25	5.674%	$251.7683	$251.77	$251.75	$251.80
Purchase #3	$52.61	3.654%	$54.5324	$54.53	$54.55	$54.50
Purchase #4	$146.50	10.616%	$162.0524	$162.05	$162.05	$162.10
Purchase #5	$248.52	13.520%	$282.1199	$282.12	$282.10	$282.10
Purchase #6	$111.79	10.837%	$123.9047	$123.90	$123.90	$123.90
Purchase #7	$9.60	5.849%	$10.1615	$10.16	$10.15	$10.20
7 purchase totals =	$918.19		$1,003.8248	$1,003.82	$1,003.80	$1,003.90