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 $216.96   13.388%   $246.0066   $246.01   $246.00   $246.00  
  Purchase #2 $205.61   13.171%   $232.6909   $232.69   $232.70   $232.70  
  Purchase #3 $118.45   3.475%   $122.5661   $122.57   $122.55   $122.60  
  Purchase #4 $104.43   7.709%   $112.4805   $112.48   $112.50   $112.50  
  Purchase #5 $21.75   11.270%   $24.2012   $24.20   $24.20   $24.20  
  Purchase #6 $21.58   5.316%   $22.7272   $22.73   $22.75   $22.70  
  Purchase #7 $158.76   10.431%   $175.3203   $175.32   $175.30   $175.30  
  7 purchase totals = $847.54       $935.9928   $936.00   $936.00   $936.00