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 $174.29   10.491%   $192.5748   $192.57   $192.55   $192.60  
  Purchase #2 $234.99   6.384%   $249.9918   $249.99   $250.00   $250.00  
  Purchase #3 $170.39   9.275%   $186.1937   $186.19   $186.20   $186.20  
  Purchase #4 $41.66   11.629%   $46.5046   $46.50   $46.50   $46.50  
  Purchase #5 $197.50   5.761%   $208.878   $208.88   $208.90   $208.90  
  Purchase #6 $149.38   12.829%   $168.544   $168.54   $168.55   $168.50  
  Purchase #7 $57.27   8.119%   $61.9198   $61.92   $61.90   $61.90  
  7 purchase totals = $1,025.48       $1,114.6067   $1,114.59   $1,114.60   $1,114.60