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	$92.78	7.670%	$99.8962	$99.90	$99.90	$99.90
Purchase #2	$69.31	12.477%	$77.9578	$77.96	$77.95	$78.00
Purchase #3	$86.82	5.607%	$91.688	$91.69	$91.70	$91.70
Purchase #4	$114.41	5.630%	$120.8513	$120.85	$120.85	$120.90
Purchase #5	$132.53	5.559%	$139.8973	$139.90	$139.90	$139.90
Purchase #6	$29.30	7.312%	$31.4424	$31.44	$31.45	$31.40
Purchase #7	$141.85	11.117%	$157.6195	$157.62	$157.60	$157.60
7 purchase totals =	$667.00		$719.3525	$719.36	$719.35	$719.40