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 $244.98   11.171%   $272.3467   $272.35   $272.35   $272.30  
  Purchase #2 $225.45   7.496%   $242.3497   $242.35   $242.35   $242.30  
  Purchase #3 $199.32   4.709%   $208.706   $208.71   $208.70   $208.70  
  Purchase #4 $49.99   12.125%   $56.0513   $56.05   $56.05   $56.10  
  Purchase #5 $232.53   8.818%   $253.0345   $253.03   $253.05   $253.00  
  Purchase #6 $140.81   7.270%   $151.0469   $151.05   $151.05   $151.00  
  Purchase #7 $73.77   6.343%   $78.4492   $78.45   $78.45   $78.40  
  7 purchase totals = $1,166.85       $1,261.9843   $1,261.99   $1,262.00   $1,261.80