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	$84.96	5.107%	$89.2989	$89.30	$89.30	$89.30
Purchase #2	$30.87	8.178%	$33.3945	$33.39	$33.40	$33.40
Purchase #3	$55.87	7.353%	$59.9781	$59.98	$60.00	$60.00
Purchase #4	$20.69	9.571%	$22.6702	$22.67	$22.65	$22.70
Purchase #5	$145.73	10.397%	$160.8815	$160.88	$160.90	$160.90
Purchase #6	$95.72	11.218%	$106.4579	$106.46	$106.45	$106.50
Purchase #7	$83.87	11.483%	$93.5008	$93.50	$93.50	$93.50
7 purchase totals =	$517.71		$566.1819	$566.18	$566.20	$566.30