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	$37.89	10.490%	$41.8647	$41.86	$41.85	$41.90
Purchase #2	$161.70	13.248%	$183.122	$183.12	$183.10	$183.10
Purchase #3	$131.84	4.572%	$137.8677	$137.87	$137.85	$137.90
Purchase #4	$230.54	6.677%	$245.9332	$245.93	$245.95	$245.90
Purchase #5	$65.82	8.647%	$71.5115	$71.51	$71.50	$71.50
Purchase #6	$30.71	9.632%	$33.668	$33.67	$33.65	$33.70
Purchase #7	$90.73	6.348%	$96.4895	$96.49	$96.50	$96.50
7 purchase totals =	$749.23		$810.4566	$810.45	$810.40	$810.50