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 $78.41   4.543%   $81.9722   $81.97   $81.95   $82.00  
  Purchase #2 $211.90   6.535%   $225.7477   $225.75   $225.75   $225.70  
  Purchase #3 $106.75   5.852%   $112.997   $113.00   $113.00   $113.00  
  Purchase #4 $109.28   9.406%   $119.5589   $119.56   $119.55   $119.60  
  Purchase #5 $156.57   5.387%   $165.0044   $165.00   $165.00   $165.00  
  Purchase #6 $56.56   10.808%   $62.673   $62.67   $62.65   $62.70  
  Purchase #7 $226.59   13.595%   $257.3949   $257.39   $257.40   $257.40  
  7 purchase totals = $946.06       $1,025.3481   $1,025.34   $1,025.30   $1,025.40