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 $201.98   6.869%   $215.854   $215.85   $215.85   $215.90  
  Purchase #2 $53.58   7.289%   $57.4854   $57.49   $57.50   $57.50  
  Purchase #3 $76.34   8.782%   $83.0442   $83.04   $83.05   $83.00  
  Purchase #4 $57.79   11.622%   $64.5064   $64.51   $64.50   $64.50  
  Purchase #5 $132.81   8.219%   $143.7257   $143.73   $143.75   $143.70  
  Purchase #6 $97.43   6.383%   $103.649   $103.65   $103.65   $103.60  
  Purchase #7 $234.25   7.670%   $252.217   $252.22   $252.20   $252.20  
  7 purchase totals = $854.18       $920.4817   $920.49   $920.50   $920.40