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	$75.42	13.339%	$85.4803	$85.48	$85.50	$85.50
Purchase #2	$65.53	11.309%	$72.9408	$72.94	$72.95	$72.90
Purchase #3	$150.57	6.508%	$160.3691	$160.37	$160.35	$160.40
Purchase #4	$250.89	11.379%	$279.4388	$279.44	$279.45	$279.40
Purchase #5	$130.74	9.683%	$143.3996	$143.40	$143.40	$143.40
Purchase #6	$157.40	11.409%	$175.3578	$175.36	$175.35	$175.40
Purchase #7	$12.28	10.414%	$13.5588	$13.56	$13.55	$13.60
7 purchase totals =	$842.83		$930.5452	$930.55	$930.55	$930.60