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 $58.66   10.373%   $64.7448   $64.74   $64.75   $64.70  
  Purchase #2 $243.89   13.602%   $277.0639   $277.06   $277.05   $277.10  
  Purchase #3 $226.69   8.352%   $245.6231   $245.62   $245.60   $245.60  
  Purchase #4 $35.98   11.531%   $40.1289   $40.13   $40.15   $40.10  
  Purchase #5 $208.70   12.786%   $235.3844   $235.38   $235.40   $235.40  
  Purchase #6 $61.72   4.662%   $64.5974   $64.60   $64.60   $64.60  
  Purchase #7 $45.34   3.270%   $46.8226   $46.82   $46.80   $46.80  
  7 purchase totals = $880.98       $974.3651   $974.35   $974.35   $974.30