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	$172.67	6.194%	$183.3652	$183.37	$183.35	$183.40
Purchase #2	$65.29	7.770%	$70.363	$70.36	$70.35	$70.40
Purchase #3	$40.73	11.753%	$45.517	$45.52	$45.50	$45.50
Purchase #4	$110.63	5.554%	$116.7744	$116.77	$116.75	$116.80
Purchase #5	$232.78	11.425%	$259.3751	$259.38	$259.40	$259.40
Purchase #6	$194.93	12.417%	$219.1345	$219.13	$219.15	$219.10
Purchase #7	$229.82	13.792%	$261.5168	$261.52	$261.50	$261.50
7 purchase totals =	$1,046.85		$1,156.0460	$1,156.05	$1,156.00	$1,156.10