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 $29.97   6.847%   $32.022   $32.02   $32.00   $32.00  
  Purchase #2 $43.56   9.546%   $47.7182   $47.72   $47.70   $47.70  
  Purchase #3 $54.77   4.397%   $57.1782   $57.18   $57.20   $57.20  
  Purchase #4 $224.47   8.423%   $243.3771   $243.38   $243.40   $243.40  
  Purchase #5 $127.70   4.311%   $133.2051   $133.21   $133.20   $133.20  
  Purchase #6 $210.87   12.222%   $236.6425   $236.64   $236.65   $236.60  
  Purchase #7 $68.33   12.788%   $77.068   $77.07   $77.05   $77.10  
  7 purchase totals = $759.67       $827.2111   $827.22   $827.20   $827.20