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	$76.46	11.683%	$85.3928	$85.39	$85.40	$85.40
Purchase #2	$158.51	3.489%	$164.0404	$164.04	$164.05	$164.00
Purchase #3	$27.50	8.716%	$29.8969	$29.90	$29.90	$29.90
Purchase #4	$38.48	8.669%	$41.8158	$41.82	$41.80	$41.80
Purchase #5	$146.89	3.845%	$152.5379	$152.54	$152.55	$152.50
Purchase #6	$133.53	10.761%	$147.8992	$147.90	$147.90	$147.90
Purchase #7	$244.84	3.663%	$253.8085	$253.81	$253.80	$253.80
7 purchase totals =	$826.21		$875.3915	$875.40	$875.40	$875.30