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	$237.35	11.192%	$263.9142	$263.91	$263.90	$263.90
Purchase #2	$51.67	3.508%	$53.4826	$53.48	$53.50	$53.50
Purchase #3	$143.82	12.694%	$162.0765	$162.08	$162.10	$162.10
Purchase #4	$26.40	7.546%	$28.3921	$28.39	$28.40	$28.40
Purchase #5	$57.79	5.611%	$61.0326	$61.03	$61.05	$61.00
Purchase #6	$87.99	13.688%	$100.0341	$100.03	$100.05	$100.00
Purchase #7	$11.57	3.160%	$11.9356	$11.94	$11.95	$11.90
7 purchase totals =	$616.59		$680.8677	$680.86	$680.95	$680.80