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	$129.84	6.496%	$138.2744	$138.27	$138.25	$138.30
Purchase #2	$215.43	6.725%	$229.9177	$229.92	$229.90	$229.90
Purchase #3	$50.30	11.248%	$55.9577	$55.96	$55.95	$56.00
Purchase #4	$132.44	13.278%	$150.0254	$150.03	$150.05	$150.00
Purchase #5	$105.34	5.821%	$111.4718	$111.47	$111.45	$111.50
Purchase #6	$165.46	4.264%	$172.5152	$172.52	$172.50	$172.50
Purchase #7	$107.89	5.330%	$113.6405	$113.64	$113.65	$113.60
7 purchase totals =	$906.70		$971.8027	$971.81	$971.75	$971.80