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	$137.46	13.842%	$156.4872	$156.49	$156.50	$156.50
Purchase #2	$174.31	9.364%	$190.6324	$190.63	$190.65	$190.60
Purchase #3	$236.65	11.388%	$263.5997	$263.60	$263.60	$263.60
Purchase #4	$86.48	12.770%	$97.5235	$97.52	$97.50	$97.50
Purchase #5	$216.76	9.128%	$236.5459	$236.55	$236.55	$236.50
Purchase #6	$52.48	13.804%	$59.7243	$59.72	$59.70	$59.70
Purchase #7	$234.83	11.717%	$262.345	$262.35	$262.35	$262.30
7 purchase totals =	$1,138.97		$1,266.8580	$1,266.86	$1,266.85	$1,266.70