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 $247.56   6.619%   $263.946   $263.95   $263.95   $263.90  
  Purchase #2 $91.43   4.835%   $95.8506   $95.85   $95.85   $95.90  
  Purchase #3 $248.54   13.597%   $282.334   $282.33   $282.35   $282.30  
  Purchase #4 $30.62   5.621%   $32.3412   $32.34   $32.35   $32.30  
  Purchase #5 $230.71   11.409%   $257.0317   $257.03   $257.05   $257.00  
  Purchase #6 $51.62   12.799%   $58.2268   $58.23   $58.25   $58.20  
  Purchase #7 $198.37   4.381%   $207.0606   $207.06   $207.05   $207.10  
  7 purchase totals = $1,098.85       $1,196.7909   $1,196.79   $1,196.85   $1,196.70