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 $121.62   5.225%   $127.9746   $127.97   $127.95   $128.00  
  Purchase #2 $179.95   10.371%   $198.6126   $198.61   $198.60   $198.60  
  Purchase #3 $231.31   6.851%   $247.157   $247.16   $247.15   $247.20  
  Purchase #4 $183.43   8.706%   $199.3994   $199.40   $199.40   $199.40  
  Purchase #5 $173.50   7.660%   $186.7901   $186.79   $186.80   $186.80  
  Purchase #6 $232.35   13.779%   $264.3655   $264.37   $264.35   $264.40  
  Purchase #7 $221.50   7.730%   $238.622   $238.62   $238.60   $238.60  
  7 purchase totals = $1,343.66       $1,462.9212   $1,462.92   $1,462.85   $1,463.00