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 $222.67   10.611%   $246.2975   $246.30   $246.30   $246.30  
  Purchase #2 $98.58   3.709%   $102.2363   $102.24   $102.25   $102.20  
  Purchase #3 $236.75   8.572%   $257.0442   $257.04   $257.05   $257.00  
  Purchase #4 $128.89   6.644%   $137.4535   $137.45   $137.45   $137.50  
  Purchase #5 $241.41   4.217%   $251.5903   $251.59   $251.60   $251.60  
  Purchase #6 $44.58   5.696%   $47.1193   $47.12   $47.10   $47.10  
  Purchase #7 $152.89   8.785%   $166.3214   $166.32   $166.30   $166.30  
  7 purchase totals = $1,125.77       $1,208.0625   $1,208.06   $1,208.05   $1,208.00