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 $82.95   10.854%   $91.9534   $91.95   $91.95   $92.00  
  Purchase #2 $103.85   5.206%   $109.2564   $109.26   $109.25   $109.30  
  Purchase #3 $69.60   12.603%   $78.3717   $78.37   $78.35   $78.40  
  Purchase #4 $168.61   10.480%   $186.2803   $186.28   $186.30   $186.30  
  Purchase #5 $56.95   6.708%   $60.7702   $60.77   $60.75   $60.80  
  Purchase #6 $72.93   3.308%   $75.3425   $75.34   $75.35   $75.30  
  Purchase #7 $20.97   3.393%   $21.6815   $21.68   $21.70   $21.70  
  7 purchase totals = $575.86       $623.6560   $623.65   $623.65   $623.80