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 $224.82   10.727%   $248.9364   $248.94   $248.95   $248.90  
  Purchase #2 $153.98   5.353%   $162.2225   $162.22   $162.20   $162.20  
  Purchase #3 $119.69   12.443%   $134.583   $134.58   $134.60   $134.60  
  Purchase #4 $175.94   8.389%   $190.6996   $190.70   $190.70   $190.70  
  Purchase #5 $150.73   13.481%   $171.0499   $171.05   $171.05   $171.00  
  Purchase #6 $234.63   12.432%   $263.7992   $263.80   $263.80   $263.80  
  Purchase #7 $152.75   13.285%   $173.0428   $173.04   $173.05   $173.00  
  7 purchase totals = $1,212.54       $1,344.3334   $1,344.33   $1,344.35   $1,344.20