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 $87.58   12.561%   $98.5809   $98.58   $98.60   $98.60  
  Purchase #2 $33.92   13.444%   $38.4802   $38.48   $38.50   $38.50  
  Purchase #3 $246.44   9.554%   $269.9849   $269.98   $270.00   $270.00  
  Purchase #4 $60.26   12.455%   $67.7654   $67.77   $67.75   $67.80  
  Purchase #5 $5.72   3.496%   $5.92   $5.92   $5.90   $5.90  
  Purchase #6 $206.63   12.821%   $233.122   $233.12   $233.10   $233.10  
  Purchase #7 $215.47   5.464%   $227.2433   $227.24   $227.25   $227.20  
  7 purchase totals = $856.02       $941.0967   $941.09   $941.10   $941.10