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 $216.45   13.506%   $245.6837   $245.68   $245.70   $245.70  
  Purchase #2 $173.47   8.169%   $187.6408   $187.64   $187.65   $187.60  
  Purchase #3 $122.67   11.146%   $136.3428   $136.34   $136.35   $136.30  
  Purchase #4 $121.67   9.474%   $133.197   $133.20   $133.20   $133.20  
  Purchase #5 $157.70   4.533%   $164.8485   $164.85   $164.85   $164.80  
  Purchase #6 $212.93   7.255%   $228.3781   $228.38   $228.40   $228.40  
  Purchase #7 $219.66   10.569%   $242.8759   $242.88   $242.90   $242.90  
  7 purchase totals = $1,224.55       $1,338.9668   $1,338.97   $1,339.05   $1,338.90