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 $92.63   6.405%   $98.563   $98.56   $98.55   $98.60  
  Purchase #2 $43.66   6.513%   $46.5036   $46.50   $46.50   $46.50  
  Purchase #3 $127.77   3.643%   $132.4247   $132.42   $132.40   $132.40  
  Purchase #4 $150.85   8.139%   $163.1277   $163.13   $163.15   $163.10  
  Purchase #5 $6.38   4.691%   $6.6793   $6.68   $6.70   $6.70  
  Purchase #6 $247.45   13.782%   $281.5536   $281.55   $281.55   $281.60  
  Purchase #7 $64.68   4.618%   $67.6669   $67.67   $67.65   $67.70  
  7 purchase totals = $733.42       $796.5188   $796.51   $796.50   $796.60