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 $96.69   12.118%   $108.4069   $108.41   $108.40   $108.40  
  Purchase #2 $89.25   4.467%   $93.2368   $93.24   $93.25   $93.20  
  Purchase #3 $14.81   11.574%   $16.5241   $16.52   $16.50   $16.50  
  Purchase #4 $117.56   4.474%   $122.8196   $122.82   $122.80   $122.80  
  Purchase #5 $125.83   10.652%   $139.2334   $139.23   $139.25   $139.20  
  Purchase #6 $133.27   13.776%   $151.6293   $151.63   $151.65   $151.60  
  Purchase #7 $85.73   7.332%   $92.0157   $92.02   $92.00   $92.00  
  7 purchase totals = $663.14       $723.8658   $723.87   $723.85   $723.70