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 $84.67   9.316%   $92.5579   $92.56   $92.55   $92.60  
  Purchase #2 $39.98   11.204%   $44.4594   $44.46   $44.45   $44.50  
  Purchase #3 $123.41   7.807%   $133.0446   $133.04   $133.05   $133.00  
  Purchase #4 $31.33   8.826%   $34.0952   $34.10   $34.10   $34.10  
  Purchase #5 $17.42   10.788%   $19.2993   $19.30   $19.30   $19.30  
  Purchase #6 $78.72   5.366%   $82.9441   $82.94   $82.95   $82.90  
  Purchase #7 $232.45   7.648%   $250.2278   $250.23   $250.25   $250.20  
  7 purchase totals = $607.98       $656.6283   $656.63   $656.65   $656.60