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	$247.27	4.457%	$258.2908	$258.29	$258.30	$258.30
Purchase #2	$230.47	11.320%	$256.5592	$256.56	$256.55	$256.60
Purchase #3	$243.77	10.161%	$268.5395	$268.54	$268.55	$268.50
Purchase #4	$66.96	7.623%	$72.0644	$72.06	$72.05	$72.10
Purchase #5	$221.34	3.653%	$229.4256	$229.43	$229.45	$229.40
Purchase #6	$140.43	13.849%	$159.8782	$159.88	$159.90	$159.90
Purchase #7	$203.93	12.357%	$229.1296	$229.13	$229.15	$229.10
7 purchase totals =	$1,354.17		$1,473.8873	$1,473.89	$1,473.95	$1,473.90