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 $241.47   13.870%   $274.9619   $274.96   $274.95   $275.00  
  Purchase #2 $59.41   6.568%   $63.312   $63.31   $63.30   $63.30  
  Purchase #3 $219.88   3.561%   $227.7099   $227.71   $227.70   $227.70  
  Purchase #4 $240.38   13.119%   $271.9155   $271.92   $271.90   $271.90  
  Purchase #5 $164.67   3.516%   $170.4598   $170.46   $170.45   $170.50  
  Purchase #6 $207.55   7.305%   $222.7115   $222.71   $222.70   $222.70  
  Purchase #7 $15.50   6.500%   $16.5075   $16.51   $16.50   $16.50  
  7 purchase totals = $1,148.86       $1,247.5781   $1,247.58   $1,247.50   $1,247.60