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	$157.91	5.639%	$166.8145	$166.81	$166.80	$166.80
Purchase #2	$45.34	4.789%	$47.5113	$47.51	$47.50	$47.50
Purchase #3	$37.43	11.803%	$41.8479	$41.85	$41.85	$41.80
Purchase #4	$243.54	11.692%	$272.0147	$272.01	$272.00	$272.00
Purchase #5	$145.46	8.387%	$157.6597	$157.66	$157.65	$157.70
Purchase #6	$122.76	4.601%	$128.4082	$128.41	$128.40	$128.40
Purchase #7	$200.72	11.477%	$223.7566	$223.76	$223.75	$223.80
7 purchase totals =	$953.16		$1,038.0129	$1,038.01	$1,037.95	$1,038.00