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	$37.92	10.789%	$42.0112	$42.01	$42.00	$42.00
Purchase #2	$160.66	7.815%	$173.2156	$173.22	$173.20	$173.20
Purchase #3	$7.72	10.145%	$8.5032	$8.50	$8.50	$8.50
Purchase #4	$139.82	11.537%	$155.951	$155.95	$155.95	$156.00
Purchase #5	$180.71	8.359%	$195.8155	$195.82	$195.80	$195.80
Purchase #6	$146.25	3.827%	$151.847	$151.85	$151.85	$151.80
Purchase #7	$73.81	6.689%	$78.7472	$78.75	$78.75	$78.70
7 purchase totals =	$746.89		$806.0907	$806.10	$806.05	$806.00