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	$130.27	5.518%	$137.4583	$137.46	$137.45	$137.50
Purchase #2	$78.98	5.870%	$83.6161	$83.62	$83.60	$83.60
Purchase #3	$135.34	13.400%	$153.4756	$153.48	$153.50	$153.50
Purchase #4	$227.71	6.401%	$242.2857	$242.29	$242.30	$242.30
Purchase #5	$71.26	10.869%	$79.0052	$79.01	$79.00	$79.00
Purchase #6	$80.83	8.258%	$87.5049	$87.50	$87.50	$87.50
Purchase #7	$231.72	13.330%	$262.6083	$262.61	$262.60	$262.60
7 purchase totals =	$956.11		$1,045.9541	$1,045.97	$1,045.95	$1,046.00