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 $59.92   5.216%   $63.0454   $63.05   $63.05   $63.00  
  Purchase #2 $98.48   11.869%   $110.1686   $110.17   $110.15   $110.20  
  Purchase #3 $27.35   5.721%   $28.9147   $28.91   $28.90   $28.90  
  Purchase #4 $32.42   12.123%   $36.3503   $36.35   $36.35   $36.40  
  Purchase #5 $195.40   11.652%   $218.168   $218.17   $218.15   $218.20  
  Purchase #6 $19.75   3.351%   $20.4118   $20.41   $20.40   $20.40  
  Purchase #7 $90.60   8.584%   $98.3771   $98.38   $98.40   $98.40  
  7 purchase totals = $523.92       $575.4359   $575.44   $575.40   $575.50