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 $165.53   12.727%   $186.597   $186.60   $186.60   $186.60  
  Purchase #2 $12.64   7.492%   $13.587   $13.59   $13.60   $13.60  
  Purchase #3 $8.56   9.534%   $9.3761   $9.38   $9.40   $9.40  
  Purchase #4 $27.42   12.115%   $30.7419   $30.74   $30.75   $30.70  
  Purchase #5 $230.39   4.307%   $240.3129   $240.31   $240.30   $240.30  
  Purchase #6 $107.90   10.605%   $119.3428   $119.34   $119.35   $119.30  
  Purchase #7 $144.74   12.523%   $162.8658   $162.87   $162.85   $162.90  
  7 purchase totals = $697.18       $762.8235   $762.83   $762.85   $762.80