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 $127.56   9.546%   $139.7369   $139.74   $139.75   $139.70  
  Purchase #2 $138.57   12.296%   $155.6086   $155.61   $155.60   $155.60  
  Purchase #3 $154.49   6.222%   $164.1024   $164.10   $164.10   $164.10  
  Purchase #4 $185.69   9.497%   $203.325   $203.33   $203.35   $203.30  
  Purchase #5 $62.28   8.863%   $67.7999   $67.80   $67.80   $67.80  
  Purchase #6 $12.26   13.464%   $13.9107   $13.91   $13.90   $13.90  
  Purchase #7 $15.51   13.222%   $17.5607   $17.56   $17.55   $17.60  
  7 purchase totals = $696.36       $762.0442   $762.05   $762.05   $762.00