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	$67.83	4.810%	$71.0926	$71.09	$71.10	$71.10
Purchase #2	$127.83	8.812%	$139.0944	$139.09	$139.10	$139.10
Purchase #3	$58.35	10.492%	$64.4721	$64.47	$64.45	$64.50
Purchase #4	$195.62	13.102%	$221.2501	$221.25	$221.25	$221.30
Purchase #5	$38.83	5.863%	$41.1066	$41.11	$41.10	$41.10
Purchase #6	$159.29	12.770%	$179.6313	$179.63	$179.65	$179.60
Purchase #7	$234.56	7.498%	$252.1473	$252.15	$252.15	$252.10
7 purchase totals =	$882.31		$968.7944	$968.79	$968.80	$968.80