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	$36.41	7.189%	$39.0275	$39.03	$39.05	$39.00
Purchase #2	$215.45	13.473%	$244.4776	$244.48	$244.50	$244.50
Purchase #3	$115.43	6.221%	$122.6109	$122.61	$122.60	$122.60
Purchase #4	$61.85	7.283%	$66.3545	$66.35	$66.35	$66.40
Purchase #5	$33.32	6.762%	$35.5731	$35.57	$35.55	$35.60
Purchase #6	$203.74	9.741%	$223.5863	$223.59	$223.60	$223.60
Purchase #7	$75.58	4.401%	$78.9063	$78.91	$78.90	$78.90
7 purchase totals =	$741.78		$810.5362	$810.54	$810.55	$810.60