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 $213.79   11.212%   $237.7601   $237.76   $237.75   $237.80  
  Purchase #2 $207.73   10.312%   $229.1511   $229.15   $229.15   $229.20  
  Purchase #3 $225.67   3.242%   $232.9862   $232.99   $233.00   $233.00  
  Purchase #4 $234.32   11.728%   $261.801   $261.80   $261.80   $261.80  
  Purchase #5 $135.91   13.517%   $154.281   $154.28   $154.30   $154.30  
  Purchase #6 $99.95   5.318%   $105.2653   $105.27   $105.25   $105.30  
  Purchase #7 $63.73   12.334%   $71.5905   $71.59   $71.60   $71.60  
  7 purchase totals = $1,181.10       $1,292.8352   $1,292.84   $1,292.85   $1,293.00