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 $44.25   12.464%   $49.7653   $49.77   $49.75   $49.80  
  Purchase #2 $171.35   12.397%   $192.5923   $192.59   $192.60   $192.60  
  Purchase #3 $230.91   6.177%   $245.1733   $245.17   $245.15   $245.20  
  Purchase #4 $215.28   5.779%   $227.721   $227.72   $227.70   $227.70  
  Purchase #5 $236.46   6.128%   $250.9503   $250.95   $250.95   $251.00  
  Purchase #6 $128.83   5.561%   $135.9942   $135.99   $136.00   $136.00  
  Purchase #7 $188.36   5.173%   $198.1039   $198.10   $198.10   $198.10  
  7 purchase totals = $1,215.44       $1,300.3003   $1,300.29   $1,300.25   $1,300.40