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	$74.30	6.110%	$78.8397	$78.84	$78.85	$78.80
Purchase #2	$83.60	8.392%	$90.6157	$90.62	$90.60	$90.60
Purchase #3	$141.32	8.373%	$153.1527	$153.15	$153.15	$153.20
Purchase #4	$81.36	3.122%	$83.9001	$83.90	$83.90	$83.90
Purchase #5	$133.43	4.150%	$138.9673	$138.97	$138.95	$139.00
Purchase #6	$199.89	11.449%	$222.7754	$222.78	$222.80	$222.80
Purchase #7	$25.97	10.127%	$28.6	$28.60	$28.60	$28.60
7 purchase totals =	$739.87		$796.8509	$796.86	$796.85	$796.90