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 $237.41   12.143%   $266.2387   $266.24   $266.25   $266.20  
  Purchase #2 $91.95   8.150%   $99.4439   $99.44   $99.45   $99.40  
  Purchase #3 $76.63   12.369%   $86.1084   $86.11   $86.10   $86.10  
  Purchase #4 $190.86   8.295%   $206.6918   $206.69   $206.70   $206.70  
  Purchase #5 $140.48   9.587%   $153.9478   $153.95   $153.95   $153.90  
  Purchase #6 $219.94   13.616%   $249.887   $249.89   $249.90   $249.90  
  Purchase #7 $57.56   5.107%   $60.4996   $60.50   $60.50   $60.50  
  7 purchase totals = $1,014.83       $1,122.8172   $1,122.82   $1,122.85   $1,122.70