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 $201.91   3.245%   $208.462   $208.46   $208.45   $208.50  
  Purchase #2 $31.90   8.259%   $34.5346   $34.53   $34.55   $34.50  
  Purchase #3 $162.98   13.826%   $185.5136   $185.51   $185.50   $185.50  
  Purchase #4 $65.49   12.411%   $73.618   $73.62   $73.60   $73.60  
  Purchase #5 $65.89   12.108%   $73.868   $73.87   $73.85   $73.90  
  Purchase #6 $246.67   13.351%   $279.6029   $279.60   $279.60   $279.60  
  Purchase #7 $51.42   5.184%   $54.0856   $54.09   $54.10   $54.10  
  7 purchase totals = $826.26       $909.6847   $909.68   $909.65   $909.70