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 $60.59   8.851%   $65.9528   $65.95   $65.95   $66.00  
  Purchase #2 $12.26   3.851%   $12.7321   $12.73   $12.75   $12.70  
  Purchase #3 $228.71   12.757%   $257.8865   $257.89   $257.90   $257.90  
  Purchase #4 $46.86   10.639%   $51.8454   $51.85   $51.85   $51.80  
  Purchase #5 $207.58   3.376%   $214.5879   $214.59   $214.60   $214.60  
  Purchase #6 $126.64   4.833%   $132.7605   $132.76   $132.75   $132.80  
  Purchase #7 $155.80   9.676%   $170.8752   $170.88   $170.90   $170.90  
  7 purchase totals = $838.44       $906.6404   $906.65   $906.70   $906.70