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	$65.52	12.666%	$73.8188	$73.82	$73.80	$73.80
Purchase #2	$190.51	13.711%	$216.6308	$216.63	$216.65	$216.60
Purchase #3	$60.84	11.653%	$67.9297	$67.93	$67.95	$67.90
Purchase #4	$37.93	11.450%	$42.273	$42.27	$42.25	$42.30
Purchase #5	$37.28	7.261%	$39.9869	$39.99	$40.00	$40.00
Purchase #6	$228.28	12.355%	$256.484	$256.48	$256.50	$256.50
Purchase #7	$226.66	6.559%	$241.5266	$241.53	$241.55	$241.50
7 purchase totals =	$847.02		$938.6498	$938.65	$938.70	$938.60