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	$68.97	13.791%	$78.4817	$78.48	$78.50	$78.50
Purchase #2	$20.79	6.526%	$22.1468	$22.15	$22.15	$22.10
Purchase #3	$163.46	4.584%	$170.953	$170.95	$170.95	$171.00
Purchase #4	$81.94	11.153%	$91.0788	$91.08	$91.10	$91.10
Purchase #5	$196.55	6.766%	$209.8486	$209.85	$209.85	$209.80
Purchase #6	$246.90	11.222%	$274.6071	$274.61	$274.60	$274.60
Purchase #7	$211.86	7.168%	$227.0461	$227.05	$227.05	$227.00
7 purchase totals =	$990.47		$1,074.1621	$1,074.17	$1,074.20	$1,074.10