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	$30.44	7.416%	$32.6974	$32.70	$32.70	$32.70
Purchase #2	$90.32	11.163%	$100.4024	$100.40	$100.40	$100.40
Purchase #3	$159.78	9.191%	$174.4654	$174.47	$174.45	$174.50
Purchase #4	$18.87	7.619%	$20.3077	$20.31	$20.30	$20.30
Purchase #5	$59.68	10.595%	$66.0031	$66.00	$66.00	$66.00
Purchase #6	$141.72	10.815%	$157.047	$157.05	$157.05	$157.00
Purchase #7	$41.25	8.821%	$44.8887	$44.89	$44.90	$44.90
7 purchase totals =	$542.06		$595.8117	$595.82	$595.80	$595.80