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 $81.88   5.265%   $86.191   $86.19   $86.20   $86.20  
  Purchase #2 $139.39   13.219%   $157.816   $157.82   $157.80   $157.80  
  Purchase #3 $222.56   7.202%   $238.5888   $238.59   $238.60   $238.60  
  Purchase #4 $65.60   11.606%   $73.2135   $73.21   $73.20   $73.20  
  Purchase #5 $160.87   5.677%   $170.0026   $170.00   $170.00   $170.00  
  Purchase #6 $133.90   9.703%   $146.8923   $146.89   $146.90   $146.90  
  Purchase #7 $94.54   4.139%   $98.453   $98.45   $98.45   $98.50  
  7 purchase totals = $898.74       $971.1572   $971.15   $971.15   $971.20