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	$39.74	6.584%	$42.3565	$42.36	$42.35	$42.40
Purchase #2	$11.73	12.304%	$13.1733	$13.17	$13.15	$13.20
Purchase #3	$120.62	8.862%	$131.3093	$131.31	$131.30	$131.30
Purchase #4	$143.93	12.793%	$162.343	$162.34	$162.35	$162.30
Purchase #5	$19.48	10.131%	$21.4535	$21.45	$21.45	$21.50
Purchase #6	$41.81	3.317%	$43.1968	$43.20	$43.20	$43.20
Purchase #7	$229.86	7.632%	$247.4029	$247.40	$247.40	$247.40
7 purchase totals =	$607.17		$661.2353	$661.23	$661.20	$661.30