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 $173.30   7.647%   $186.5523   $186.55   $186.55   $186.60  
  Purchase #2 $246.44   8.410%   $267.1656   $267.17   $267.15   $267.20  
  Purchase #3 $127.27   12.498%   $143.1762   $143.18   $143.20   $143.20  
  Purchase #4 $182.59   6.861%   $195.1175   $195.12   $195.10   $195.10  
  Purchase #5 $83.71   7.426%   $89.9263   $89.93   $89.95   $89.90  
  Purchase #6 $38.42   13.340%   $43.5452   $43.55   $43.55   $43.50  
  Purchase #7 $175.68   10.161%   $193.5308   $193.53   $193.55   $193.50  
  7 purchase totals = $1,027.41       $1,119.0139   $1,119.03   $1,119.05   $1,119.00