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	$243.36	11.279%	$270.8086	$270.81	$270.80	$270.80
Purchase #2	$60.92	10.207%	$67.1381	$67.14	$67.15	$67.10
Purchase #3	$10.96	8.255%	$11.8647	$11.86	$11.85	$11.90
Purchase #4	$136.48	6.849%	$145.8275	$145.83	$145.85	$145.80
Purchase #5	$74.47	5.636%	$78.6671	$78.67	$78.65	$78.70
Purchase #6	$48.26	4.780%	$50.5668	$50.57	$50.55	$50.60
Purchase #7	$66.55	6.840%	$71.102	$71.10	$71.10	$71.10
7 purchase totals =	$641.00		$695.9748	$695.98	$695.95	$696.00