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 $93.92   4.744%   $98.3756   $98.38   $98.40   $98.40  
  Purchase #2 $232.90   4.255%   $242.8099   $242.81   $242.80   $242.80  
  Purchase #3 $247.42   6.179%   $262.7081   $262.71   $262.70   $262.70  
  Purchase #4 $207.35   3.757%   $215.1401   $215.14   $215.15   $215.10  
  Purchase #5 $11.38   4.282%   $11.8673   $11.87   $11.85   $11.90  
  Purchase #6 $128.63   6.355%   $136.8044   $136.80   $136.80   $136.80  
  Purchase #7 $95.86   5.499%   $101.1313   $101.13   $101.15   $101.10  
  7 purchase totals = $1,017.46       $1,068.8367   $1,068.84   $1,068.85   $1,068.80