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 $48.60   10.811%   $53.8541   $53.85   $53.85   $53.90  
  Purchase #2 $91.55   11.254%   $101.853   $101.85   $101.85   $101.90  
  Purchase #3 $151.45   12.387%   $170.2101   $170.21   $170.20   $170.20  
  Purchase #4 $71.99   8.684%   $78.2416   $78.24   $78.25   $78.20  
  Purchase #5 $214.62   11.447%   $239.1876   $239.19   $239.20   $239.20  
  Purchase #6 $81.47   3.660%   $84.4518   $84.45   $84.45   $84.50  
  Purchase #7 $65.93   4.335%   $68.7881   $68.79   $68.80   $68.80  
  7 purchase totals = $725.61       $796.5863   $796.58   $796.60   $796.70