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 $118.70   12.327%   $133.3321   $133.33   $133.35   $133.30  
  Purchase #2 $172.73   10.781%   $191.352   $191.35   $191.35   $191.40  
  Purchase #3 $59.49   10.532%   $65.7555   $65.76   $65.75   $65.80  
  Purchase #4 $164.93   6.688%   $175.9605   $175.96   $175.95   $176.00  
  Purchase #5 $42.53   10.630%   $47.0509   $47.05   $47.05   $47.10  
  Purchase #6 $239.46   13.682%   $272.2229   $272.22   $272.20   $272.20  
  Purchase #7 $35.81   12.588%   $40.3178   $40.32   $40.30   $40.30  
  7 purchase totals = $833.65       $925.9917   $925.99   $925.95   $926.10