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 $31.30   12.110%   $35.0904   $35.09   $35.10   $35.10  
  Purchase #2 $91.66   4.302%   $95.6032   $95.60   $95.60   $95.60  
  Purchase #3 $43.98   7.290%   $47.1861   $47.19   $47.20   $47.20  
  Purchase #4 $191.66   12.511%   $215.6386   $215.64   $215.65   $215.60  
  Purchase #5 $211.63   12.311%   $237.6838   $237.68   $237.70   $237.70  
  Purchase #6 $62.66   4.597%   $65.5405   $65.54   $65.55   $65.50  
  Purchase #7 $250.38   7.166%   $268.3222   $268.32   $268.30   $268.30  
  7 purchase totals = $883.27       $965.0648   $965.06   $965.10   $965.00