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	$166.43	3.468%	$172.2018	$172.20	$172.20	$172.20
Purchase #2	$38.33	3.453%	$39.6535	$39.65	$39.65	$39.70
Purchase #3	$170.34	12.460%	$191.5644	$191.56	$191.55	$191.60
Purchase #4	$194.40	12.461%	$218.6242	$218.62	$218.60	$218.60
Purchase #5	$7.98	6.869%	$8.5281	$8.53	$8.55	$8.50
Purchase #6	$37.97	12.790%	$42.8264	$42.83	$42.85	$42.80
Purchase #7	$89.98	5.853%	$95.2465	$95.25	$95.25	$95.20
7 purchase totals =	$705.43		$768.6449	$768.64	$768.65	$768.60