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	$38.32	9.659%	$42.0213	$42.02	$42.00	$42.00
Purchase #2	$82.48	11.686%	$92.1186	$92.12	$92.10	$92.10
Purchase #3	$88.34	10.671%	$97.7668	$97.77	$97.75	$97.80
Purchase #4	$17.42	6.387%	$18.5326	$18.53	$18.55	$18.50
Purchase #5	$91.92	7.233%	$98.5686	$98.57	$98.55	$98.60
Purchase #6	$83.83	6.532%	$89.3058	$89.31	$89.30	$89.30
Purchase #7	$37.29	11.267%	$41.4915	$41.49	$41.50	$41.50
7 purchase totals =	$439.60		$479.8052	$479.81	$479.75	$479.80