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	$34.52	6.649%	$36.8152	$36.82	$36.80	$36.80
Purchase #2	$221.64	11.528%	$247.1907	$247.19	$247.20	$247.20
Purchase #3	$80.31	7.673%	$86.4722	$86.47	$86.45	$86.50
Purchase #4	$50.46	7.834%	$54.413	$54.41	$54.40	$54.40
Purchase #5	$122.73	6.639%	$130.878	$130.88	$130.90	$130.90
Purchase #6	$150.45	12.236%	$168.8591	$168.86	$168.85	$168.90
Purchase #7	$228.31	6.340%	$242.7849	$242.78	$242.80	$242.80
7 purchase totals =	$888.42		$967.4131	$967.41	$967.40	$967.50