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	$120.88	13.769%	$137.524	$137.52	$137.50	$137.50
Purchase #2	$40.38	8.222%	$43.7	$43.70	$43.70	$43.70
Purchase #3	$170.57	13.213%	$193.1074	$193.11	$193.10	$193.10
Purchase #4	$194.55	7.368%	$208.8844	$208.88	$208.90	$208.90
Purchase #5	$232.59	9.822%	$255.435	$255.44	$255.45	$255.40
Purchase #6	$27.33	11.460%	$30.462	$30.46	$30.45	$30.50
Purchase #7	$54.30	9.434%	$59.4227	$59.42	$59.40	$59.40
7 purchase totals =	$840.60		$928.5355	$928.53	$928.50	$928.50