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	$42.55	6.670%	$45.3881	$45.39	$45.40	$45.40
Purchase #2	$223.89	13.642%	$254.4331	$254.43	$254.45	$254.40
Purchase #3	$111.32	8.484%	$120.7644	$120.76	$120.75	$120.80
Purchase #4	$190.49	4.856%	$199.7402	$199.74	$199.75	$199.70
Purchase #5	$141.79	5.333%	$149.3517	$149.35	$149.35	$149.40
Purchase #6	$163.79	3.523%	$169.5603	$169.56	$169.55	$169.60
Purchase #7	$191.82	4.270%	$200.0107	$200.01	$200.00	$200.00
7 purchase totals =	$1,065.65		$1,139.2485	$1,139.24	$1,139.25	$1,139.30