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 $24.38   9.761%   $26.7597   $26.76   $26.75   $26.80  
  Purchase #2 $232.36   4.454%   $242.7093   $242.71   $242.70   $242.70  
  Purchase #3 $244.77   7.665%   $263.5316   $263.53   $263.55   $263.50  
  Purchase #4 $102.69   9.209%   $112.1467   $112.15   $112.15   $112.10  
  Purchase #5 $103.40   5.515%   $109.1025   $109.10   $109.10   $109.10  
  Purchase #6 $214.63   9.268%   $234.5219   $234.52   $234.50   $234.50  
  Purchase #7 $208.39   3.184%   $215.0251   $215.03   $215.05   $215.00  
  7 purchase totals = $1,130.62       $1,203.7968   $1,203.80   $1,203.80   $1,203.70