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 $55.59   4.827%   $58.2733   $58.27   $58.25   $58.30  
  Purchase #2 $48.44   8.537%   $52.5753   $52.58   $52.60   $52.60  
  Purchase #3 $27.43   7.773%   $29.5621   $29.56   $29.55   $29.60  
  Purchase #4 $157.66   9.315%   $172.346   $172.35   $172.35   $172.30  
  Purchase #5 $191.27   12.401%   $214.9894   $214.99   $215.00   $215.00  
  Purchase #6 $228.98   8.786%   $249.0982   $249.10   $249.10   $249.10  
  Purchase #7 $250.88   6.526%   $267.2524   $267.25   $267.25   $267.30  
  7 purchase totals = $960.25       $1,044.0967   $1,044.10   $1,044.10   $1,044.20