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 $58.82   4.730%   $61.6022   $61.60   $61.60   $61.60  
  Purchase #2 $45.51   12.332%   $51.1223   $51.12   $51.10   $51.10  
  Purchase #3 $17.62   10.215%   $19.4199   $19.42   $19.40   $19.40  
  Purchase #4 $37.37   11.739%   $41.7569   $41.76   $41.75   $41.80  
  Purchase #5 $72.80   6.720%   $77.6922   $77.69   $77.70   $77.70  
  Purchase #6 $175.98   10.462%   $194.391   $194.39   $194.40   $194.40  
  Purchase #7 $82.56   11.706%   $92.2245   $92.22   $92.20   $92.20  
  7 purchase totals = $490.66       $538.2090   $538.20   $538.15   $538.20