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	$40.50	9.770%	$44.4569	$44.46	$44.45	$44.50
Purchase #2	$160.67	6.456%	$171.0429	$171.04	$171.05	$171.00
Purchase #3	$223.50	13.698%	$254.115	$254.12	$254.10	$254.10
Purchase #4	$7.59	4.277%	$7.9146	$7.91	$7.90	$7.90
Purchase #5	$81.68	8.824%	$88.8874	$88.89	$88.90	$88.90
Purchase #6	$197.78	13.120%	$223.7287	$223.73	$223.75	$223.70
Purchase #7	$64.46	9.354%	$70.4896	$70.49	$70.50	$70.50
7 purchase totals =	$776.18		$860.6351	$860.64	$860.65	$860.60