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	$99.48	9.138%	$108.5705	$108.57	$108.55	$108.60
Purchase #2	$232.66	10.263%	$256.5379	$256.54	$256.55	$256.50
Purchase #3	$202.70	3.272%	$209.3323	$209.33	$209.35	$209.30
Purchase #4	$160.48	5.267%	$168.9325	$168.93	$168.95	$168.90
Purchase #5	$85.61	13.637%	$97.2846	$97.28	$97.30	$97.30
Purchase #6	$20.42	5.776%	$21.5995	$21.60	$21.60	$21.60
Purchase #7	$217.45	4.800%	$227.8876	$227.89	$227.90	$227.90
7 purchase totals =	$1,018.80		$1,090.1449	$1,090.14	$1,090.20	$1,090.10