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	$172.48	11.248%	$191.8806	$191.88	$191.90	$191.90
Purchase #2	$75.93	7.764%	$81.8252	$81.83	$81.85	$81.80
Purchase #3	$209.30	11.481%	$233.3297	$233.33	$233.35	$233.30
Purchase #4	$23.89	8.294%	$25.8714	$25.87	$25.85	$25.90
Purchase #5	$248.47	10.356%	$274.2016	$274.20	$274.20	$274.20
Purchase #6	$44.81	12.857%	$50.5712	$50.57	$50.55	$50.60
Purchase #7	$11.71	7.553%	$12.5945	$12.59	$12.60	$12.60
7 purchase totals =	$786.59		$870.2742	$870.27	$870.30	$870.30