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 $24.76   8.779%   $26.9337   $26.93   $26.95   $26.90  
  Purchase #2 $107.40   7.278%   $115.2166   $115.22   $115.20   $115.20  
  Purchase #3 $17.25   11.627%   $19.2557   $19.26   $19.25   $19.30  
  Purchase #4 $13.89   10.628%   $15.3662   $15.37   $15.35   $15.40  
  Purchase #5 $242.53   9.314%   $265.1192   $265.12   $265.10   $265.10  
  Purchase #6 $60.53   3.414%   $62.5965   $62.60   $62.60   $62.60  
  Purchase #7 $235.73   10.276%   $259.9536   $259.95   $259.95   $260.00  
  7 purchase totals = $702.09       $764.4415   $764.45   $764.40   $764.50