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 $64.25   3.217%   $66.3169   $66.32   $66.30   $66.30  
  Purchase #2 $231.59   11.552%   $258.3433   $258.34   $258.35   $258.30  
  Purchase #3 $126.91   11.847%   $141.945   $141.95   $141.95   $141.90  
  Purchase #4 $72.47   4.696%   $75.8732   $75.87   $75.85   $75.90  
  Purchase #5 $6.42   3.301%   $6.6319   $6.63   $6.65   $6.60  
  Purchase #6 $55.41   5.258%   $58.3235   $58.32   $58.30   $58.30  
  Purchase #7 $186.91   7.150%   $200.2741   $200.27   $200.25   $200.30  
  7 purchase totals = $743.96       $807.7079   $807.70   $807.65   $807.60