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	$113.72	6.316%	$120.9026	$120.90	$120.90	$120.90
Purchase #2	$60.29	3.465%	$62.379	$62.38	$62.40	$62.40
Purchase #3	$233.47	6.492%	$248.6269	$248.63	$248.65	$248.60
Purchase #4	$151.70	6.703%	$161.8685	$161.87	$161.85	$161.90
Purchase #5	$55.53	6.810%	$59.3116	$59.31	$59.30	$59.30
Purchase #6	$129.67	13.685%	$147.4153	$147.42	$147.40	$147.40
Purchase #7	$106.52	11.134%	$118.3799	$118.38	$118.40	$118.40
7 purchase totals =	$850.90		$918.8838	$918.89	$918.90	$918.90