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 $208.92   12.196%   $234.3999   $234.40   $234.40   $234.40  
  Purchase #2 $44.69   11.580%   $49.8651   $49.87   $49.85   $49.90  
  Purchase #3 $177.70   10.758%   $196.817   $196.82   $196.80   $196.80  
  Purchase #4 $240.33   6.630%   $256.2639   $256.26   $256.25   $256.30  
  Purchase #5 $158.70   10.540%   $175.427   $175.43   $175.45   $175.40  
  Purchase #6 $162.65   10.483%   $179.7006   $179.70   $179.70   $179.70  
  Purchase #7 $167.66   5.134%   $176.2677   $176.27   $176.25   $176.30  
  7 purchase totals = $1,160.65       $1,268.7412   $1,268.75   $1,268.70   $1,268.80