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 $71.67   11.111%   $79.6333   $79.63   $79.65   $79.60  
  Purchase #2 $114.55   7.304%   $122.9167   $122.92   $122.90   $122.90  
  Purchase #3 $231.60   7.749%   $249.5467   $249.55   $249.55   $249.50  
  Purchase #4 $244.42   7.449%   $262.6268   $262.63   $262.65   $262.60  
  Purchase #5 $134.63   12.337%   $151.2393   $151.24   $151.25   $151.20  
  Purchase #6 $111.33   5.640%   $117.609   $117.61   $117.60   $117.60  
  Purchase #7 $104.73   6.549%   $111.5888   $111.59   $111.60   $111.60  
  7 purchase totals = $1,012.93       $1,095.1606   $1,095.17   $1,095.20   $1,095.00