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 $246.76   3.227%   $254.7229   $254.72   $254.70   $254.70  
  Purchase #2 $119.95   4.299%   $125.1067   $125.11   $125.10   $125.10  
  Purchase #3 $165.77   4.342%   $172.9677   $172.97   $172.95   $173.00  
  Purchase #4 $19.69   9.830%   $21.6255   $21.63   $21.65   $21.60  
  Purchase #5 $52.53   8.782%   $57.1432   $57.14   $57.15   $57.10  
  Purchase #6 $38.94   11.706%   $43.4983   $43.50   $43.50   $43.50  
  Purchase #7 $59.90   9.202%   $65.412   $65.41   $65.40   $65.40  
  7 purchase totals = $703.54       $740.4763   $740.48   $740.45   $740.40