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	$125.46	13.727%	$142.6819	$142.68	$142.70	$142.70
Purchase #2	$91.27	11.829%	$102.0663	$102.07	$102.05	$102.10
Purchase #3	$186.78	4.451%	$195.0936	$195.09	$195.10	$195.10
Purchase #4	$57.96	5.523%	$61.1611	$61.16	$61.15	$61.20
Purchase #5	$25.49	11.635%	$28.4558	$28.46	$28.45	$28.50
Purchase #6	$18.45	12.155%	$20.6926	$20.69	$20.70	$20.70
Purchase #7	$113.40	13.146%	$128.3076	$128.31	$128.30	$128.30
7 purchase totals =	$618.81		$678.4589	$678.46	$678.45	$678.60