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	$33.57	6.575%	$35.7772	$35.78	$35.80	$35.80
Purchase #2	$131.70	6.741%	$140.5779	$140.58	$140.60	$140.60
Purchase #3	$83.44	8.606%	$90.6208	$90.62	$90.60	$90.60
Purchase #4	$74.46	10.336%	$82.1562	$82.16	$82.15	$82.20
Purchase #5	$244.89	11.148%	$272.1903	$272.19	$272.20	$272.20
Purchase #6	$41.27	5.318%	$43.4647	$43.46	$43.45	$43.50
Purchase #7	$147.61	7.399%	$158.5317	$158.53	$158.55	$158.50
7 purchase totals =	$756.94		$823.3188	$823.32	$823.35	$823.40