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 $113.71   10.577%   $125.7371   $125.74   $125.75   $125.70  
  Purchase #2 $59.90   13.432%   $67.9458   $67.95   $67.95   $67.90  
  Purchase #3 $26.74   9.212%   $29.2033   $29.20   $29.20   $29.20  
  Purchase #4 $165.94   8.394%   $179.869   $179.87   $179.85   $179.90  
  Purchase #5 $76.77   6.408%   $81.6894   $81.69   $81.70   $81.70  
  Purchase #6 $192.79   13.480%   $218.7781   $218.78   $218.80   $218.80  
  Purchase #7 $62.34   11.718%   $69.645   $69.65   $69.65   $69.60  
  7 purchase totals = $698.19       $772.8677   $772.88   $772.90   $772.80