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	$142.56	11.276%	$158.6351	$158.64	$158.65	$158.60
Purchase #2	$74.34	12.775%	$83.8369	$83.84	$83.85	$83.80
Purchase #3	$234.89	8.797%	$255.5533	$255.55	$255.55	$255.60
Purchase #4	$32.88	3.781%	$34.1232	$34.12	$34.10	$34.10
Purchase #5	$83.49	9.862%	$91.7238	$91.72	$91.70	$91.70
Purchase #6	$145.55	5.650%	$153.7736	$153.77	$153.75	$153.80
Purchase #7	$171.78	11.265%	$191.131	$191.13	$191.15	$191.10
7 purchase totals =	$885.49		$968.7769	$968.77	$968.75	$968.70