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	$170.95	8.545%	$185.5577	$185.56	$185.55	$185.60
Purchase #2	$33.84	5.626%	$35.7438	$35.74	$35.75	$35.70
Purchase #3	$219.83	9.443%	$240.5885	$240.59	$240.60	$240.60
Purchase #4	$64.66	8.833%	$70.3714	$70.37	$70.35	$70.40
Purchase #5	$171.46	7.527%	$184.3658	$184.37	$184.35	$184.40
Purchase #6	$143.29	5.383%	$151.0033	$151.00	$151.00	$151.00
Purchase #7	$98.49	11.517%	$109.8331	$109.83	$109.85	$109.80
7 purchase totals =	$902.52		$977.4636	$977.46	$977.45	$977.50