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 $37.59   9.612%   $41.2032   $41.20   $41.20   $41.20  
  Purchase #2 $250.66   6.106%   $265.9653   $265.97   $265.95   $266.00  
  Purchase #3 $190.59   4.353%   $198.8864   $198.89   $198.90   $198.90  
  Purchase #4 $175.99   5.254%   $185.2365   $185.24   $185.25   $185.20  
  Purchase #5 $171.86   4.402%   $179.4253   $179.43   $179.45   $179.40  
  Purchase #6 $198.43   3.246%   $204.871   $204.87   $204.85   $204.90  
  Purchase #7 $225.89   3.152%   $233.0101   $233.01   $233.00   $233.00  
  7 purchase totals = $1,251.01       $1,308.5978   $1,308.61   $1,308.60   $1,308.60