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	$13.59	10.642%	$15.0362	$15.04	$15.05	$15.00
Purchase #2	$68.61	4.449%	$71.6625	$71.66	$71.65	$71.70
Purchase #3	$140.91	7.104%	$150.9202	$150.92	$150.90	$150.90
Purchase #4	$209.73	6.273%	$222.8864	$222.89	$222.90	$222.90
Purchase #5	$13.40	3.592%	$13.8813	$13.88	$13.90	$13.90
Purchase #6	$208.73	10.383%	$230.4024	$230.40	$230.40	$230.40
Purchase #7	$89.30	6.494%	$95.0991	$95.10	$95.10	$95.10
7 purchase totals =	$744.27		$799.8881	$799.89	$799.90	$799.90