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	$44.26	13.254%	$50.1262	$50.13	$50.15	$50.10
Purchase #2	$151.40	13.495%	$171.8314	$171.83	$171.85	$171.80
Purchase #3	$6.25	5.664%	$6.604	$6.60	$6.60	$6.60
Purchase #4	$227.96	13.369%	$258.436	$258.44	$258.45	$258.40
Purchase #5	$78.53	6.779%	$83.8535	$83.85	$83.85	$83.90
Purchase #6	$111.50	12.576%	$125.5222	$125.52	$125.50	$125.50
Purchase #7	$130.94	9.272%	$143.0808	$143.08	$143.10	$143.10
7 purchase totals =	$750.84		$839.4541	$839.45	$839.50	$839.40