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 $244.86   5.680%   $258.768   $258.77   $258.75   $258.80  
  Purchase #2 $163.62   3.319%   $169.0505   $169.05   $169.05   $169.10  
  Purchase #3 $138.57   4.377%   $144.6352   $144.64   $144.65   $144.60  
  Purchase #4 $78.38   13.851%   $89.2364   $89.24   $89.25   $89.20  
  Purchase #5 $240.44   12.664%   $270.8893   $270.89   $270.90   $270.90  
  Purchase #6 $42.35   6.767%   $45.2158   $45.22   $45.20   $45.20  
  Purchase #7 $201.80   10.854%   $223.7034   $223.70   $223.70   $223.70  
  7 purchase totals = $1,110.02       $1,201.4986   $1,201.51   $1,201.50   $1,201.50