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 $125.33   7.681%   $134.9566   $134.96   $134.95   $135.00  
  Purchase #2 $246.49   11.308%   $274.3631   $274.36   $274.35   $274.40  
  Purchase #3 $111.85   4.592%   $116.9862   $116.99   $117.00   $117.00  
  Purchase #4 $214.39   8.223%   $232.0193   $232.02   $232.00   $232.00  
  Purchase #5 $42.49   12.180%   $47.6653   $47.67   $47.65   $47.70  
  Purchase #6 $113.33   11.733%   $126.627   $126.63   $126.65   $126.60  
  Purchase #7 $9.55   11.539%   $10.652   $10.65   $10.65   $10.70  
  7 purchase totals = $863.43       $943.2695   $943.28   $943.25   $943.40