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	$129.53	7.807%	$139.6424	$139.64	$139.65	$139.60
Purchase #2	$6.55	7.738%	$7.0568	$7.06	$7.05	$7.10
Purchase #3	$210.32	8.117%	$227.3917	$227.39	$227.40	$227.40
Purchase #4	$168.61	4.489%	$176.1789	$176.18	$176.20	$176.20
Purchase #5	$237.41	7.578%	$255.4009	$255.40	$255.40	$255.40
Purchase #6	$80.61	13.870%	$91.7906	$91.79	$91.80	$91.80
Purchase #7	$40.48	13.427%	$45.9152	$45.92	$45.90	$45.90
7 purchase totals =	$873.51		$943.3765	$943.38	$943.40	$943.40