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	$32.55	3.769%	$33.7768	$33.78	$33.80	$33.80
Purchase #2	$198.89	6.705%	$212.2256	$212.23	$212.25	$212.20
Purchase #3	$137.56	9.205%	$150.2224	$150.22	$150.20	$150.20
Purchase #4	$159.44	8.125%	$172.3945	$172.39	$172.40	$172.40
Purchase #5	$116.66	8.263%	$126.2996	$126.30	$126.30	$126.30
Purchase #6	$36.74	13.863%	$41.8333	$41.83	$41.85	$41.80
Purchase #7	$44.52	13.387%	$50.4799	$50.48	$50.50	$50.50
7 purchase totals =	$726.36		$787.2321	$787.23	$787.30	$787.20