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	$77.68	9.698%	$85.2134	$85.21	$85.20	$85.20
Purchase #2	$204.27	6.736%	$218.0296	$218.03	$218.05	$218.00
Purchase #3	$26.38	7.503%	$28.3593	$28.36	$28.35	$28.40
Purchase #4	$28.94	8.103%	$31.285	$31.29	$31.30	$31.30
Purchase #5	$198.57	12.788%	$223.9631	$223.96	$223.95	$224.00
Purchase #6	$134.70	11.597%	$150.3212	$150.32	$150.30	$150.30
Purchase #7	$40.28	13.357%	$45.6602	$45.66	$45.65	$45.70
7 purchase totals =	$710.82		$782.8318	$782.83	$782.80	$782.90