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 $239.53   7.312%   $257.0444   $257.04   $257.05   $257.00  
  Purchase #2 $169.47   7.490%   $182.1633   $182.16   $182.15   $182.20  
  Purchase #3 $111.95   11.343%   $124.6485   $124.65   $124.65   $124.60  
  Purchase #4 $168.25   11.671%   $187.8865   $187.89   $187.90   $187.90  
  Purchase #5 $103.73   8.673%   $112.7265   $112.73   $112.75   $112.70  
  Purchase #6 $117.46   11.615%   $131.103   $131.10   $131.10   $131.10  
  Purchase #7 $163.88   6.504%   $174.5388   $174.54   $174.55   $174.50  
  7 purchase totals = $1,074.27       $1,170.1110   $1,170.11   $1,170.15   $1,170.00