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 $49.80   7.621%   $53.5953   $53.60   $53.60   $53.60  
  Purchase #2 $228.74   11.209%   $254.3795   $254.38   $254.40   $254.40  
  Purchase #3 $246.70   9.508%   $270.1562   $270.16   $270.15   $270.20  
  Purchase #4 $38.49   6.299%   $40.9145   $40.91   $40.90   $40.90  
  Purchase #5 $35.42   11.172%   $39.3771   $39.38   $39.40   $39.40  
  Purchase #6 $242.53   4.206%   $252.7308   $252.73   $252.75   $252.70  
  Purchase #7 $195.34   5.815%   $206.699   $206.70   $206.70   $206.70  
  7 purchase totals = $1,037.02       $1,117.8524   $1,117.86   $1,117.90   $1,117.90