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 $67.85   13.373%   $76.9236   $76.92   $76.90   $76.90  
  Purchase #2 $231.54   11.862%   $259.0053   $259.01   $259.00   $259.00  
  Purchase #3 $239.49   4.493%   $250.2503   $250.25   $250.25   $250.30  
  Purchase #4 $120.75   11.462%   $134.5904   $134.59   $134.60   $134.60  
  Purchase #5 $62.45   6.144%   $66.2869   $66.29   $66.30   $66.30  
  Purchase #6 $179.47   13.800%   $204.2369   $204.24   $204.25   $204.20  
  Purchase #7 $103.77   3.143%   $107.0315   $107.03   $107.05   $107.00  
  7 purchase totals = $1,005.32       $1,098.3249   $1,098.33   $1,098.35   $1,098.30