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	$230.43	11.399%	$256.6967	$256.70	$256.70	$256.70
Purchase #2	$73.34	12.408%	$82.44	$82.44	$82.45	$82.40
Purchase #3	$58.25	11.281%	$64.8212	$64.82	$64.80	$64.80
Purchase #4	$30.57	4.768%	$32.0276	$32.03	$32.05	$32.00
Purchase #5	$7.41	6.541%	$7.8947	$7.89	$7.90	$7.90
Purchase #6	$34.30	11.143%	$38.122	$38.12	$38.10	$38.10
Purchase #7	$48.76	13.811%	$55.4942	$55.49	$55.50	$55.50
7 purchase totals =	$483.06		$537.4964	$537.49	$537.50	$537.40