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	$183.54	12.445%	$206.3816	$206.38	$206.40	$206.40
Purchase #2	$65.46	9.500%	$71.6787	$71.68	$71.70	$71.70
Purchase #3	$105.63	10.130%	$116.3303	$116.33	$116.35	$116.30
Purchase #4	$55.49	9.417%	$60.7155	$60.72	$60.70	$60.70
Purchase #5	$61.52	9.440%	$67.3275	$67.33	$67.35	$67.30
Purchase #6	$200.67	11.430%	$223.6066	$223.61	$223.60	$223.60
Purchase #7	$153.75	7.503%	$165.2859	$165.29	$165.30	$165.30
7 purchase totals =	$826.06		$911.3261	$911.34	$911.40	$911.30