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	$223.45	11.636%	$249.4506	$249.45	$249.45	$249.50
Purchase #2	$190.83	12.522%	$214.7257	$214.73	$214.75	$214.70
Purchase #3	$186.78	5.223%	$196.5355	$196.54	$196.55	$196.50
Purchase #4	$144.57	10.610%	$159.9089	$159.91	$159.90	$159.90
Purchase #5	$140.55	6.672%	$149.9275	$149.93	$149.95	$149.90
Purchase #6	$159.82	7.384%	$171.6211	$171.62	$171.60	$171.60
Purchase #7	$119.30	11.765%	$133.3356	$133.34	$133.35	$133.30
7 purchase totals =	$1,165.30		$1,275.5049	$1,275.52	$1,275.55	$1,275.40