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	$32.95	12.870%	$37.1907	$37.19	$37.20	$37.20
Purchase #2	$248.58	6.232%	$264.0715	$264.07	$264.05	$264.10
Purchase #3	$103.90	7.731%	$111.9325	$111.93	$111.95	$111.90
Purchase #4	$68.26	9.188%	$74.5317	$74.53	$74.55	$74.50
Purchase #5	$145.64	13.759%	$165.6786	$165.68	$165.70	$165.70
Purchase #6	$31.78	13.322%	$36.0137	$36.01	$36.00	$36.00
Purchase #7	$131.30	6.182%	$139.417	$139.42	$139.40	$139.40
7 purchase totals =	$762.41		$828.8357	$828.83	$828.85	$828.80