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	$78.74	8.738%	$85.6203	$85.62	$85.60	$85.60
Purchase #2	$201.86	12.855%	$227.8091	$227.81	$227.80	$227.80
Purchase #3	$164.58	9.738%	$180.6068	$180.61	$180.60	$180.60
Purchase #4	$21.67	12.225%	$24.3192	$24.32	$24.30	$24.30
Purchase #5	$92.27	6.354%	$98.1328	$98.13	$98.15	$98.10
Purchase #6	$38.51	10.603%	$42.5932	$42.59	$42.60	$42.60
Purchase #7	$209.74	11.648%	$234.1705	$234.17	$234.15	$234.20
7 purchase totals =	$807.37		$893.2519	$893.25	$893.20	$893.20