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 $9.90   5.545%   $10.449   $10.45   $10.45   $10.40  
  Purchase #2 $73.67   6.821%   $78.695   $78.70   $78.70   $78.70  
  Purchase #3 $182.29   8.788%   $198.3096   $198.31   $198.30   $198.30  
  Purchase #4 $10.73   13.359%   $12.1634   $12.16   $12.15   $12.20  
  Purchase #5 $80.44   10.665%   $89.0189   $89.02   $89.00   $89.00  
  Purchase #6 $220.36   5.284%   $232.0038   $232.00   $232.00   $232.00  
  Purchase #7 $109.94   12.838%   $124.0541   $124.05   $124.05   $124.10  
  7 purchase totals = $687.33       $744.6938   $744.69   $744.65   $744.70