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	$34.27	9.324%	$37.4653	$37.47	$37.45	$37.50
Purchase #2	$39.59	5.437%	$41.7425	$41.74	$41.75	$41.70
Purchase #3	$168.94	13.781%	$192.2216	$192.22	$192.20	$192.20
Purchase #4	$124.40	12.777%	$140.2946	$140.29	$140.30	$140.30
Purchase #5	$152.37	6.473%	$162.2329	$162.23	$162.25	$162.20
Purchase #6	$93.55	6.733%	$99.8487	$99.85	$99.85	$99.80
Purchase #7	$11.77	8.405%	$12.7593	$12.76	$12.75	$12.80
7 purchase totals =	$624.89		$686.5649	$686.56	$686.55	$686.50