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	$52.37	13.369%	$59.3713	$59.37	$59.35	$59.40
Purchase #2	$140.27	13.332%	$158.9708	$158.97	$158.95	$159.00
Purchase #3	$48.51	7.489%	$52.1429	$52.14	$52.15	$52.10
Purchase #4	$209.27	3.850%	$217.3269	$217.33	$217.35	$217.30
Purchase #5	$174.33	8.635%	$189.3834	$189.38	$189.40	$189.40
Purchase #6	$237.92	4.675%	$249.0428	$249.04	$249.05	$249.00
Purchase #7	$127.87	13.394%	$144.9969	$145.00	$145.00	$145.00
7 purchase totals =	$990.54		$1,071.2350	$1,071.23	$1,071.25	$1,071.20