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 $246.82   4.226%   $257.2506   $257.25   $257.25   $257.30  
  Purchase #2 $131.70   11.415%   $146.7336   $146.73   $146.75   $146.70  
  Purchase #3 $42.53   9.299%   $46.4849   $46.48   $46.50   $46.50  
  Purchase #4 $240.64   7.286%   $258.173   $258.17   $258.15   $258.20  
  Purchase #5 $77.38   3.457%   $80.055   $80.06   $80.05   $80.10  
  Purchase #6 $217.68   9.857%   $239.1367   $239.14   $239.15   $239.10  
  Purchase #7 $213.95   9.296%   $233.8388   $233.84   $233.85   $233.80  
  7 purchase totals = $1,170.70       $1,261.6726   $1,261.67   $1,261.70   $1,261.70