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 $233.47   10.373%   $257.6878   $257.69   $257.70   $257.70  
  Purchase #2 $39.93   9.526%   $43.7337   $43.73   $43.75   $43.70  
  Purchase #3 $153.62   13.186%   $173.8763   $173.88   $173.90   $173.90  
  Purchase #4 $250.25   8.280%   $270.9707   $270.97   $270.95   $271.00  
  Purchase #5 $245.76   12.143%   $275.6026   $275.60   $275.60   $275.60  
  Purchase #6 $216.49   4.689%   $226.6412   $226.64   $226.65   $226.60  
  Purchase #7 $69.95   12.868%   $78.9512   $78.95   $78.95   $79.00  
  7 purchase totals = $1,209.47       $1,327.4635   $1,327.46   $1,327.50   $1,327.50