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	$105.38	11.346%	$117.3364	$117.34	$117.35	$117.30
Purchase #2	$171.43	5.135%	$180.2329	$180.23	$180.25	$180.20
Purchase #3	$158.56	13.402%	$179.8102	$179.81	$179.80	$179.80
Purchase #4	$219.48	4.412%	$229.1635	$229.16	$229.15	$229.20
Purchase #5	$141.67	7.232%	$151.9156	$151.92	$151.90	$151.90
Purchase #6	$54.67	8.336%	$59.2273	$59.23	$59.25	$59.20
Purchase #7	$20.72	13.499%	$23.517	$23.52	$23.50	$23.50
7 purchase totals =	$871.91		$941.2029	$941.21	$941.20	$941.10