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 $213.77   13.820%   $243.313   $243.31   $243.30   $243.30  
  Purchase #2 $186.86   11.673%   $208.6722   $208.67   $208.65   $208.70  
  Purchase #3 $207.34   4.189%   $216.0255   $216.03   $216.05   $216.00  
  Purchase #4 $91.90   4.799%   $96.3103   $96.31   $96.30   $96.30  
  Purchase #5 $158.65   12.734%   $178.8525   $178.85   $178.85   $178.90  
  Purchase #6 $234.67   11.305%   $261.1994   $261.20   $261.20   $261.20  
  Purchase #7 $74.91   4.379%   $78.1903   $78.19   $78.20   $78.20  
  7 purchase totals = $1,168.10       $1,282.5632   $1,282.56   $1,282.55   $1,282.60