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 $83.37   13.301%   $94.459   $94.46   $94.45   $94.50  
  Purchase #2 $133.47   10.153%   $147.0212   $147.02   $147.00   $147.00  
  Purchase #3 $109.61   4.809%   $114.8811   $114.88   $114.90   $114.90  
  Purchase #4 $92.68   8.115%   $100.201   $100.20   $100.20   $100.20  
  Purchase #5 $121.31   10.353%   $133.8692   $133.87   $133.85   $133.90  
  Purchase #6 $104.58   5.484%   $110.3152   $110.32   $110.30   $110.30  
  Purchase #7 $64.64   4.387%   $67.4758   $67.48   $67.50   $67.50  
  7 purchase totals = $709.66       $768.2225   $768.23   $768.20   $768.30