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 $235.84   13.465%   $267.5959   $267.60   $267.60   $267.60  
  Purchase #2 $210.80   10.285%   $232.4808   $232.48   $232.50   $232.50  
  Purchase #3 $20.46   5.648%   $21.6156   $21.62   $21.60   $21.60  
  Purchase #4 $49.68   7.343%   $53.328   $53.33   $53.35   $53.30  
  Purchase #5 $221.34   10.728%   $245.0854   $245.09   $245.10   $245.10  
  Purchase #6 $242.99   4.208%   $253.215   $253.22   $253.20   $253.20  
  Purchase #7 $113.39   5.569%   $119.7047   $119.70   $119.70   $119.70  
  7 purchase totals = $1,094.50       $1,193.0254   $1,193.04   $1,193.05   $1,193.00