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	$82.79	8.462%	$89.7957	$89.80	$89.80	$89.80
Purchase #2	$30.77	6.528%	$32.7787	$32.78	$32.80	$32.80
Purchase #3	$28.92	4.733%	$30.2888	$30.29	$30.30	$30.30
Purchase #4	$179.45	9.335%	$196.2017	$196.20	$196.20	$196.20
Purchase #5	$43.31	5.873%	$45.8536	$45.85	$45.85	$45.90
Purchase #6	$167.29	12.363%	$187.9721	$187.97	$187.95	$188.00
Purchase #7	$8.38	5.612%	$8.8503	$8.85	$8.85	$8.90
7 purchase totals =	$540.91		$591.7409	$591.74	$591.75	$591.90