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 $232.34   12.623%   $261.6683   $261.67   $261.65   $261.70  
  Purchase #2 $164.56   13.615%   $186.9648   $186.96   $186.95   $187.00  
  Purchase #3 $249.45   10.367%   $275.3105   $275.31   $275.30   $275.30  
  Purchase #4 $172.47   11.469%   $192.2506   $192.25   $192.25   $192.30  
  Purchase #5 $246.49   3.118%   $254.1756   $254.18   $254.20   $254.20  
  Purchase #6 $182.61   7.434%   $196.1852   $196.19   $196.20   $196.20  
  Purchase #7 $94.38   8.856%   $102.7383   $102.74   $102.75   $102.70  
  7 purchase totals = $1,342.30       $1,469.2933   $1,469.30   $1,469.30   $1,469.40