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 $197.46   9.644%   $216.503   $216.50   $216.50   $216.50  
  Purchase #2 $15.74   8.104%   $17.0156   $17.02   $17.00   $17.00  
  Purchase #3 $70.66   10.685%   $78.21   $78.21   $78.20   $78.20  
  Purchase #4 $128.51   5.826%   $135.997   $136.00   $136.00   $136.00  
  Purchase #5 $57.70   6.394%   $61.3893   $61.39   $61.40   $61.40  
  Purchase #6 $170.28   10.650%   $188.4148   $188.41   $188.40   $188.40  
  Purchase #7 $169.53   3.524%   $175.5042   $175.50   $175.50   $175.50  
  7 purchase totals = $809.88       $873.0339   $873.03   $873.00   $873.00