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	$233.99	9.638%	$256.542	$256.54	$256.55	$256.50
Purchase #2	$100.52	4.624%	$105.168	$105.17	$105.15	$105.20
Purchase #3	$195.96	6.357%	$208.4172	$208.42	$208.40	$208.40
Purchase #4	$217.65	11.764%	$243.2543	$243.25	$243.25	$243.30
Purchase #5	$93.97	12.307%	$105.5349	$105.53	$105.55	$105.50
Purchase #6	$247.28	8.371%	$267.9798	$267.98	$268.00	$268.00
Purchase #7	$131.79	4.389%	$137.5743	$137.57	$137.55	$137.60
7 purchase totals =	$1,221.16		$1,324.4705	$1,324.46	$1,324.45	$1,324.50