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	$199.90	8.409%	$216.7096	$216.71	$216.70	$216.70
Purchase #2	$74.76	4.742%	$78.3051	$78.31	$78.30	$78.30
Purchase #3	$183.31	11.527%	$204.4401	$204.44	$204.45	$204.40
Purchase #4	$161.43	12.448%	$181.5248	$181.52	$181.50	$181.50
Purchase #5	$47.62	5.519%	$50.2481	$50.25	$50.25	$50.20
Purchase #6	$46.81	4.535%	$48.9328	$48.93	$48.95	$48.90
Purchase #7	$84.57	7.321%	$90.7614	$90.76	$90.75	$90.80
7 purchase totals =	$798.40		$870.9219	$870.92	$870.90	$870.80