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 $58.67   8.709%   $63.7796   $63.78   $63.80   $63.80  
  Purchase #2 $225.74   3.611%   $233.8915   $233.89   $233.90   $233.90  
  Purchase #3 $8.62   3.578%   $8.9284   $8.93   $8.95   $8.90  
  Purchase #4 $53.69   5.364%   $56.5699   $56.57   $56.55   $56.60  
  Purchase #5 $78.60   12.250%   $88.2285   $88.23   $88.25   $88.20  
  Purchase #6 $179.47   13.418%   $203.5513   $203.55   $203.55   $203.60  
  Purchase #7 $199.83   7.339%   $214.4955   $214.50   $214.50   $214.50  
  7 purchase totals = $804.62       $869.4447   $869.45   $869.50   $869.50