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	$90.98	5.753%	$96.2141	$96.21	$96.20	$96.20
Purchase #2	$72.30	8.390%	$78.366	$78.37	$78.35	$78.40
Purchase #3	$113.79	9.190%	$124.2473	$124.25	$124.25	$124.20
Purchase #4	$35.43	12.502%	$39.8595	$39.86	$39.85	$39.90
Purchase #5	$158.93	4.118%	$165.4747	$165.47	$165.45	$165.50
Purchase #6	$40.89	9.463%	$44.7594	$44.76	$44.75	$44.80
Purchase #7	$96.47	12.510%	$108.5384	$108.54	$108.55	$108.50
7 purchase totals =	$608.79		$657.4594	$657.46	$657.40	$657.50