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 $244.70   8.776%   $266.1749   $266.17   $266.15   $266.20  
  Purchase #2 $157.73   11.228%   $175.4399   $175.44   $175.45   $175.40  
  Purchase #3 $177.38   5.722%   $187.5297   $187.53   $187.55   $187.50  
  Purchase #4 $90.89   13.236%   $102.9202   $102.92   $102.90   $102.90  
  Purchase #5 $125.65   4.696%   $131.5505   $131.55   $131.55   $131.60  
  Purchase #6 $119.57   5.343%   $125.9586   $125.96   $125.95   $126.00  
  Purchase #7 $241.67   11.154%   $268.6259   $268.63   $268.65   $268.60  
  7 purchase totals = $1,157.59       $1,258.1997   $1,258.20   $1,258.20   $1,258.20