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	$59.59	12.791%	$67.2122	$67.21	$67.20	$67.20
Purchase #2	$31.50	4.204%	$32.8243	$32.82	$32.80	$32.80
Purchase #3	$220.90	8.298%	$239.2303	$239.23	$239.25	$239.20
Purchase #4	$72.27	4.154%	$75.2721	$75.27	$75.25	$75.30
Purchase #5	$170.99	5.467%	$180.338	$180.34	$180.35	$180.30
Purchase #6	$164.42	10.124%	$181.0659	$181.07	$181.05	$181.10
Purchase #7	$243.89	4.697%	$255.3455	$255.35	$255.35	$255.30
7 purchase totals =	$963.56		$1,031.2883	$1,031.29	$1,031.25	$1,031.20