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 $162.66   12.476%   $182.9535   $182.95   $182.95   $183.00  
  Purchase #2 $110.73   7.524%   $119.0613   $119.06   $119.05   $119.10  
  Purchase #3 $57.46   9.414%   $62.8693   $62.87   $62.85   $62.90  
  Purchase #4 $175.44   3.323%   $181.2699   $181.27   $181.25   $181.30  
  Purchase #5 $82.93   11.750%   $92.6743   $92.67   $92.65   $92.70  
  Purchase #6 $236.48   5.825%   $250.255   $250.26   $250.25   $250.30  
  Purchase #7 $59.48   4.567%   $62.1965   $62.20   $62.20   $62.20  
  7 purchase totals = $885.18       $951.2798   $951.28   $951.20   $951.50