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	$150.64	13.173%	$170.4838	$170.48	$170.50	$170.50
Purchase #2	$141.86	11.168%	$157.7029	$157.70	$157.70	$157.70
Purchase #3	$219.89	13.461%	$249.4894	$249.49	$249.50	$249.50
Purchase #4	$174.72	12.731%	$196.9636	$196.96	$196.95	$197.00
Purchase #5	$239.42	3.149%	$246.9593	$246.96	$246.95	$247.00
Purchase #6	$167.38	3.182%	$172.706	$172.71	$172.70	$172.70
Purchase #7	$77.75	10.245%	$85.7155	$85.72	$85.70	$85.70
7 purchase totals =	$1,171.66		$1,280.0205	$1,280.02	$1,280.00	$1,280.10