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 $116.91   13.111%   $132.2381   $132.24   $132.25   $132.20  
  Purchase #2 $206.37   11.602%   $230.313   $230.31   $230.30   $230.30  
  Purchase #3 $124.27   5.578%   $131.2018   $131.20   $131.20   $131.20  
  Purchase #4 $40.95   5.155%   $43.061   $43.06   $43.05   $43.10  
  Purchase #5 $171.90   13.548%   $195.189   $195.19   $195.20   $195.20  
  Purchase #6 $6.42   6.448%   $6.834   $6.83   $6.85   $6.80  
  Purchase #7 $56.49   4.743%   $59.1693   $59.17   $59.15   $59.20  
  7 purchase totals = $723.31       $798.0062   $798.00   $798.00   $798.00