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	$166.81	4.644%	$174.5567	$174.56	$174.55	$174.60
Purchase #2	$156.99	5.153%	$165.0797	$165.08	$165.10	$165.10
Purchase #3	$250.71	11.500%	$279.5417	$279.54	$279.55	$279.50
Purchase #4	$212.72	7.809%	$229.3313	$229.33	$229.35	$229.30
Purchase #5	$240.47	6.467%	$256.0212	$256.02	$256.00	$256.00
Purchase #6	$12.86	3.616%	$13.325	$13.33	$13.35	$13.30
Purchase #7	$108.82	6.761%	$116.1773	$116.18	$116.20	$116.20
7 purchase totals =	$1,149.38		$1,234.0329	$1,234.04	$1,234.10	$1,234.00