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 $53.83   8.584%   $58.4508   $58.45   $58.45   $58.50  
  Purchase #2 $161.56   11.106%   $179.5029   $179.50   $179.50   $179.50  
  Purchase #3 $127.99   4.257%   $133.4385   $133.44   $133.45   $133.40  
  Purchase #4 $226.26   11.807%   $252.9745   $252.97   $252.95   $253.00  
  Purchase #5 $110.65   8.229%   $119.7554   $119.76   $119.75   $119.80  
  Purchase #6 $44.38   6.373%   $47.2083   $47.21   $47.20   $47.20  
  Purchase #7 $242.78   13.309%   $275.0916   $275.09   $275.10   $275.10  
  7 purchase totals = $967.45       $1,066.4220   $1,066.42   $1,066.40   $1,066.50