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 $87.84   5.822%   $92.954   $92.95   $92.95   $93.00  
  Purchase #2 $24.84   9.527%   $27.2065   $27.21   $27.20   $27.20  
  Purchase #3 $194.49   13.640%   $221.0184   $221.02   $221.00   $221.00  
  Purchase #4 $154.36   5.713%   $163.1786   $163.18   $163.20   $163.20  
  Purchase #5 $55.38   11.117%   $61.5366   $61.54   $61.55   $61.50  
  Purchase #6 $107.91   13.609%   $122.5955   $122.60   $122.60   $122.60  
  Purchase #7 $137.75   10.869%   $152.722   $152.72   $152.70   $152.70  
  7 purchase totals = $762.57       $841.2116   $841.22   $841.20   $841.20