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	$80.83	10.444%	$89.2719	$89.27	$89.25	$89.30
Purchase #2	$114.38	10.641%	$126.5512	$126.55	$126.55	$126.60
Purchase #3	$118.30	8.255%	$128.0657	$128.07	$128.05	$128.10
Purchase #4	$43.35	4.574%	$45.3328	$45.33	$45.35	$45.30
Purchase #5	$229.85	7.670%	$247.4795	$247.48	$247.50	$247.50
Purchase #6	$157.53	9.114%	$171.8873	$171.89	$171.90	$171.90
Purchase #7	$119.75	13.525%	$135.9462	$135.95	$135.95	$135.90
7 purchase totals =	$863.99		$944.5346	$944.54	$944.55	$944.60