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	$58.31	6.819%	$62.2862	$62.29	$62.30	$62.30
Purchase #2	$135.28	6.109%	$143.5443	$143.54	$143.55	$143.50
Purchase #3	$175.43	8.641%	$190.5889	$190.59	$190.60	$190.60
Purchase #4	$207.35	11.438%	$231.0667	$231.07	$231.05	$231.10
Purchase #5	$113.74	8.543%	$123.4568	$123.46	$123.45	$123.50
Purchase #6	$58.86	13.560%	$66.8414	$66.84	$66.85	$66.80
Purchase #7	$109.51	7.577%	$117.8076	$117.81	$117.80	$117.80
7 purchase totals =	$858.48		$935.5919	$935.60	$935.60	$935.60