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	$106.43	6.491%	$113.3384	$113.34	$113.35	$113.30
Purchase #2	$76.82	12.826%	$86.6729	$86.67	$86.65	$86.70
Purchase #3	$110.57	6.185%	$117.4088	$117.41	$117.40	$117.40
Purchase #4	$80.25	4.169%	$83.5956	$83.60	$83.60	$83.60
Purchase #5	$55.43	10.460%	$61.228	$61.23	$61.25	$61.20
Purchase #6	$38.94	8.728%	$42.3387	$42.34	$42.35	$42.30
Purchase #7	$159.32	5.575%	$168.2021	$168.20	$168.20	$168.20
7 purchase totals =	$627.76		$672.7845	$672.79	$672.80	$672.70