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 $224.64   10.696%   $248.6675   $248.67   $248.65   $248.70  
  Purchase #2 $96.72   8.134%   $104.5872   $104.59   $104.60   $104.60  
  Purchase #3 $64.97   13.737%   $73.8949   $73.89   $73.90   $73.90  
  Purchase #4 $84.85   12.663%   $95.5946   $95.59   $95.60   $95.60  
  Purchase #5 $164.63   11.265%   $183.1756   $183.18   $183.20   $183.20  
  Purchase #6 $29.33   5.659%   $30.9898   $30.99   $31.00   $31.00  
  Purchase #7 $30.32   8.181%   $32.8005   $32.80   $32.80   $32.80  
  7 purchase totals = $695.46       $769.7101   $769.71   $769.75   $769.80