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	$66.50	13.250%	$75.3113	$75.31	$75.30	$75.30
Purchase #2	$184.53	5.582%	$194.8305	$194.83	$194.85	$194.80
Purchase #3	$160.90	7.182%	$172.4558	$172.46	$172.45	$172.50
Purchase #4	$245.64	12.452%	$276.2271	$276.23	$276.25	$276.20
Purchase #5	$208.70	11.122%	$231.9116	$231.91	$231.90	$231.90
Purchase #6	$150.48	3.330%	$155.491	$155.49	$155.50	$155.50
Purchase #7	$117.98	8.385%	$127.8726	$127.87	$127.85	$127.90
7 purchase totals =	$1,134.73		$1,234.0999	$1,234.10	$1,234.10	$1,234.10