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 $196.87   4.109%   $204.9594   $204.96   $204.95   $205.00  
  Purchase #2 $189.95   5.745%   $200.8626   $200.86   $200.85   $200.90  
  Purchase #3 $126.92   11.716%   $141.7899   $141.79   $141.80   $141.80  
  Purchase #4 $55.47   9.549%   $60.7668   $60.77   $60.75   $60.80  
  Purchase #5 $108.42   4.196%   $112.9693   $112.97   $112.95   $113.00  
  Purchase #6 $178.29   8.154%   $192.8278   $192.83   $192.85   $192.80  
  Purchase #7 $70.25   4.815%   $73.6325   $73.63   $73.65   $73.60  
  7 purchase totals = $926.17       $987.8083   $987.81   $987.80   $987.90