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	$166.61	12.525%	$187.4779	$187.48	$187.50	$187.50
Purchase #2	$97.42	8.467%	$105.6686	$105.67	$105.65	$105.70
Purchase #3	$221.44	7.571%	$238.2052	$238.21	$238.20	$238.20
Purchase #4	$45.47	11.426%	$50.6654	$50.67	$50.65	$50.70
Purchase #5	$157.38	13.692%	$178.9285	$178.93	$178.95	$178.90
Purchase #6	$215.61	8.422%	$233.7687	$233.77	$233.75	$233.80
Purchase #7	$238.46	7.201%	$255.6315	$255.63	$255.65	$255.60
7 purchase totals =	$1,142.39		$1,250.3458	$1,250.36	$1,250.35	$1,250.40