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 $39.86   8.535%   $43.2621   $43.26   $43.25   $43.30  
  Purchase #2 $149.53   10.542%   $165.2935   $165.29   $165.30   $165.30  
  Purchase #3 $85.58   10.697%   $94.7345   $94.73   $94.75   $94.70  
  Purchase #4 $64.58   13.802%   $73.4933   $73.49   $73.50   $73.50  
  Purchase #5 $163.47   8.363%   $177.141   $177.14   $177.15   $177.10  
  Purchase #6 $16.94   4.186%   $17.6491   $17.65   $17.65   $17.60  
  Purchase #7 $164.83   5.382%   $173.7012   $173.70   $173.70   $173.70  
  7 purchase totals = $684.79       $745.2747   $745.26   $745.30   $745.20