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	$81.99	10.861%	$90.8949	$90.89	$90.90	$90.90
Purchase #2	$27.45	5.485%	$28.9556	$28.96	$28.95	$29.00
Purchase #3	$155.77	5.835%	$164.8592	$164.86	$164.85	$164.90
Purchase #4	$25.42	8.123%	$27.4849	$27.48	$27.50	$27.50
Purchase #5	$130.27	6.180%	$138.3207	$138.32	$138.30	$138.30
Purchase #6	$139.54	6.184%	$148.1692	$148.17	$148.15	$148.20
Purchase #7	$199.67	13.706%	$227.0368	$227.04	$227.05	$227.00
7 purchase totals =	$760.11		$825.7213	$825.72	$825.70	$825.80