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	$86.48	4.503%	$90.3742	$90.37	$90.35	$90.40
Purchase #2	$147.35	6.648%	$157.1458	$157.15	$157.15	$157.10
Purchase #3	$139.92	12.500%	$157.41	$157.41	$157.40	$157.40
Purchase #4	$115.32	9.708%	$126.5153	$126.52	$126.50	$126.50
Purchase #5	$54.94	12.244%	$61.6669	$61.67	$61.65	$61.70
Purchase #6	$37.82	12.110%	$42.4	$42.40	$42.40	$42.40
Purchase #7	$119.88	7.644%	$129.0436	$129.04	$129.05	$129.00
7 purchase totals =	$701.71		$764.5558	$764.56	$764.50	$764.50