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 $145.85   6.584%   $155.4528   $155.45   $155.45   $155.50  
  Purchase #2 $152.75   3.805%   $158.5621   $158.56   $158.55   $158.60  
  Purchase #3 $176.89   10.841%   $196.0666   $196.07   $196.05   $196.10  
  Purchase #4 $187.62   8.533%   $203.6296   $203.63   $203.65   $203.60  
  Purchase #5 $241.82   3.614%   $250.5594   $250.56   $250.55   $250.60  
  Purchase #6 $117.27   7.231%   $125.7498   $125.75   $125.75   $125.70  
  Purchase #7 $104.96   12.628%   $118.2143   $118.21   $118.20   $118.20  
  7 purchase totals = $1,127.16       $1,208.2346   $1,208.23   $1,208.20   $1,208.30