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	$189.96	4.233%	$198.001	$198.00	$198.00	$198.00
Purchase #2	$174.43	8.471%	$189.206	$189.21	$189.20	$189.20
Purchase #3	$147.72	13.825%	$168.1423	$168.14	$168.15	$168.10
Purchase #4	$96.49	4.518%	$100.8494	$100.85	$100.85	$100.80
Purchase #5	$83.76	13.450%	$95.0257	$95.03	$95.05	$95.00
Purchase #6	$82.59	3.648%	$85.6029	$85.60	$85.60	$85.60
Purchase #7	$63.32	4.294%	$66.039	$66.04	$66.05	$66.00
7 purchase totals =	$838.27		$902.8663	$902.87	$902.90	$902.70