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 $113.49   3.534%   $117.5007   $117.50   $117.50   $117.50  
  Purchase #2 $60.98   12.620%   $68.6757   $68.68   $68.70   $68.70  
  Purchase #3 $200.31   13.295%   $226.9412   $226.94   $226.95   $226.90  
  Purchase #4 $189.42   10.826%   $209.9266   $209.93   $209.95   $209.90  
  Purchase #5 $42.29   9.309%   $46.2268   $46.23   $46.25   $46.20  
  Purchase #6 $13.89   3.535%   $14.381   $14.38   $14.40   $14.40  
  Purchase #7 $142.76   4.730%   $149.5125   $149.51   $149.50   $149.50  
  7 purchase totals = $763.14       $833.1645   $833.17   $833.25   $833.10