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	$81.42	9.805%	$89.4032	$89.40	$89.40	$89.40
Purchase #2	$23.54	6.692%	$25.1153	$25.12	$25.10	$25.10
Purchase #3	$214.60	8.332%	$232.4805	$232.48	$232.50	$232.50
Purchase #4	$206.60	3.473%	$213.7752	$213.78	$213.80	$213.80
Purchase #5	$6.82	5.752%	$7.2123	$7.21	$7.20	$7.20
Purchase #6	$75.39	9.282%	$82.3877	$82.39	$82.40	$82.40
Purchase #7	$242.61	13.559%	$275.5055	$275.51	$275.50	$275.50
7 purchase totals =	$850.98		$925.8797	$925.89	$925.90	$925.90