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 $120.27   13.281%   $136.2431   $136.24   $136.25   $136.20  
  Purchase #2 $132.71   7.500%   $142.6633   $142.66   $142.65   $142.70  
  Purchase #3 $179.81   5.770%   $190.185   $190.19   $190.20   $190.20  
  Purchase #4 $115.69   9.652%   $126.8564   $126.86   $126.85   $126.90  
  Purchase #5 $144.81   11.669%   $161.7079   $161.71   $161.70   $161.70  
  Purchase #6 $197.96   7.561%   $212.9278   $212.93   $212.95   $212.90  
  Purchase #7 $100.79   5.241%   $106.0724   $106.07   $106.05   $106.10  
  7 purchase totals = $992.04       $1,076.6559   $1,076.66   $1,076.65   $1,076.70