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 $98.85   6.728%   $105.5006   $105.50   $105.50   $105.50  
  Purchase #2 $187.36   11.123%   $208.2001   $208.20   $208.20   $208.20  
  Purchase #3 $5.93   12.250%   $6.6564   $6.66   $6.65   $6.70  
  Purchase #4 $115.55   3.714%   $119.8415   $119.84   $119.85   $119.80  
  Purchase #5 $18.26   13.148%   $20.6608   $20.66   $20.65   $20.70  
  Purchase #6 $58.57   4.315%   $61.0973   $61.10   $61.10   $61.10  
  Purchase #7 $232.62   12.411%   $261.4905   $261.49   $261.50   $261.50  
  7 purchase totals = $717.14       $783.4472   $783.45   $783.45   $783.50