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 $61.44   3.177%   $63.3919   $63.39   $63.40   $63.40  
  Purchase #2 $54.29   6.129%   $57.6174   $57.62   $57.60   $57.60  
  Purchase #3 $122.48   7.821%   $132.0592   $132.06   $132.05   $132.10  
  Purchase #4 $32.38   11.395%   $36.0697   $36.07   $36.05   $36.10  
  Purchase #5 $61.42   13.771%   $69.8781   $69.88   $69.90   $69.90  
  Purchase #6 $68.58   10.373%   $75.6938   $75.69   $75.70   $75.70  
  Purchase #7 $204.80   10.757%   $226.8303   $226.83   $226.85   $226.80  
  7 purchase totals = $605.39       $661.5404   $661.54   $661.55   $661.60