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	$192.33	5.730%	$203.3505	$203.35	$203.35	$203.40
Purchase #2	$90.68	5.633%	$95.788	$95.79	$95.80	$95.80
Purchase #3	$57.35	13.413%	$65.0424	$65.04	$65.05	$65.00
Purchase #4	$32.69	3.602%	$33.8675	$33.87	$33.85	$33.90
Purchase #5	$10.30	5.745%	$10.8917	$10.89	$10.90	$10.90
Purchase #6	$94.66	6.642%	$100.9473	$100.95	$100.95	$100.90
Purchase #7	$139.39	13.340%	$157.9846	$157.98	$158.00	$158.00
7 purchase totals =	$617.40		$667.8720	$667.87	$667.90	$667.90