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	$90.62	6.634%	$96.6317	$96.63	$96.65	$96.60
Purchase #2	$32.73	9.652%	$35.8891	$35.89	$35.90	$35.90
Purchase #3	$203.85	11.195%	$226.671	$226.67	$226.65	$226.70
Purchase #4	$219.59	10.520%	$242.6909	$242.69	$242.70	$242.70
Purchase #5	$174.72	9.146%	$190.6999	$190.70	$190.70	$190.70
Purchase #6	$18.76	12.772%	$21.156	$21.16	$21.15	$21.20
Purchase #7	$91.25	9.775%	$100.1697	$100.17	$100.15	$100.20
7 purchase totals =	$831.52		$913.9083	$913.91	$913.90	$914.00