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 $241.47   5.671%   $255.1638   $255.16   $255.15   $255.20  
  Purchase #2 $126.71   7.119%   $135.7305   $135.73   $135.75   $135.70  
  Purchase #3 $201.45   3.235%   $207.9669   $207.97   $207.95   $208.00  
  Purchase #4 $73.45   11.489%   $81.8887   $81.89   $81.90   $81.90  
  Purchase #5 $22.97   11.631%   $25.6416   $25.64   $25.65   $25.60  
  Purchase #6 $244.34   8.739%   $265.6929   $265.69   $265.70   $265.70  
  Purchase #7 $247.88   3.244%   $255.9212   $255.92   $255.90   $255.90  
  7 purchase totals = $1,158.27       $1,228.0056   $1,228.00   $1,228.00   $1,228.00