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 $186.90   6.506%   $199.0597   $199.06   $199.05   $199.10  
  Purchase #2 $223.94   12.617%   $252.1945   $252.19   $252.20   $252.20  
  Purchase #3 $232.67   8.294%   $251.9676   $251.97   $251.95   $252.00  
  Purchase #4 $117.48   4.508%   $122.776   $122.78   $122.80   $122.80  
  Purchase #5 $88.81   11.333%   $98.8748   $98.87   $98.85   $98.90  
  Purchase #6 $144.45   5.541%   $152.454   $152.45   $152.45   $152.50  
  Purchase #7 $59.93   10.134%   $66.0033   $66.00   $66.00   $66.00  
  7 purchase totals = $1,054.18       $1,143.3299   $1,143.32   $1,143.30   $1,143.50