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	$19.71	7.558%	$21.1997	$21.20	$21.20	$21.20
Purchase #2	$179.46	11.347%	$199.8233	$199.82	$199.80	$199.80
Purchase #3	$153.33	8.228%	$165.946	$165.95	$165.95	$165.90
Purchase #4	$103.72	7.349%	$111.3424	$111.34	$111.35	$111.30
Purchase #5	$249.89	8.833%	$271.9628	$271.96	$271.95	$272.00
Purchase #6	$75.95	8.133%	$82.127	$82.13	$82.15	$82.10
Purchase #7	$121.29	10.537%	$134.0703	$134.07	$134.05	$134.10
7 purchase totals =	$903.35		$986.4715	$986.47	$986.45	$986.40