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 $23.99   8.511%   $26.0318   $26.03   $26.05   $26.00  
  Purchase #2 $92.68   13.840%   $105.5069   $105.51   $105.50   $105.50  
  Purchase #3 $247.75   5.211%   $260.6603   $260.66   $260.65   $260.70  
  Purchase #4 $97.35   6.329%   $103.5113   $103.51   $103.50   $103.50  
  Purchase #5 $153.54   6.550%   $163.5969   $163.60   $163.60   $163.60  
  Purchase #6 $105.40   3.439%   $109.0247   $109.02   $109.00   $109.00  
  Purchase #7 $167.64   13.175%   $189.7266   $189.73   $189.75   $189.70  
  7 purchase totals = $888.35       $958.0585   $958.06   $958.05   $958.00