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	$121.27	13.373%	$137.4874	$137.49	$137.50	$137.50
Purchase #2	$203.34	10.115%	$223.9078	$223.91	$223.90	$223.90
Purchase #3	$93.90	12.529%	$105.6647	$105.66	$105.65	$105.70
Purchase #4	$105.78	4.524%	$110.5655	$110.57	$110.55	$110.60
Purchase #5	$17.60	10.769%	$19.4953	$19.50	$19.50	$19.50
Purchase #6	$99.92	4.548%	$104.4644	$104.46	$104.45	$104.50
Purchase #7	$144.81	10.353%	$159.8022	$159.80	$159.80	$159.80
7 purchase totals =	$786.62		$861.3873	$861.39	$861.35	$861.50