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	$61.57	10.508%	$68.0398	$68.04	$68.05	$68.00
Purchase #2	$142.52	5.419%	$150.2432	$150.24	$150.25	$150.20
Purchase #3	$67.86	6.762%	$72.4487	$72.45	$72.45	$72.40
Purchase #4	$200.41	12.377%	$225.2147	$225.21	$225.20	$225.20
Purchase #5	$125.74	12.344%	$141.2613	$141.26	$141.25	$141.30
Purchase #6	$41.59	10.624%	$46.0085	$46.01	$46.00	$46.00
Purchase #7	$35.73	5.609%	$37.7341	$37.73	$37.75	$37.70
7 purchase totals =	$675.42		$740.9503	$740.94	$740.95	$740.80