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	$93.38	6.708%	$99.6439	$99.64	$99.65	$99.60
Purchase #2	$241.98	5.741%	$255.8721	$255.87	$255.85	$255.90
Purchase #3	$46.58	13.859%	$53.0355	$53.04	$53.05	$53.00
Purchase #4	$28.64	11.468%	$31.9244	$31.92	$31.90	$31.90
Purchase #5	$69.89	10.811%	$77.4458	$77.45	$77.45	$77.40
Purchase #6	$15.31	8.121%	$16.5533	$16.55	$16.55	$16.60
Purchase #7	$59.43	10.853%	$65.8799	$65.88	$65.90	$65.90
7 purchase totals =	$555.21		$600.3549	$600.35	$600.35	$600.30