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 $45.49   6.538%   $48.4641   $48.46   $48.45   $48.50  
  Purchase #2 $123.87   12.471%   $139.3178   $139.32   $139.30   $139.30  
  Purchase #3 $164.26   12.800%   $185.2853   $185.29   $185.30   $185.30  
  Purchase #4 $113.94   4.677%   $119.269   $119.27   $119.25   $119.30  
  Purchase #5 $75.39   3.393%   $77.948   $77.95   $77.95   $77.90  
  Purchase #6 $10.65   6.120%   $11.3018   $11.30   $11.30   $11.30  
  Purchase #7 $227.64   8.161%   $246.2177   $246.22   $246.20   $246.20  
  7 purchase totals = $761.24       $827.8037   $827.81   $827.75   $827.80