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 $56.38   5.733%   $59.6123   $59.61   $59.60   $59.60  
  Purchase #2 $181.74   8.854%   $197.8313   $197.83   $197.85   $197.80  
  Purchase #3 $13.25   3.718%   $13.7426   $13.74   $13.75   $13.70  
  Purchase #4 $13.53   3.555%   $14.011   $14.01   $14.00   $14.00  
  Purchase #5 $55.70   3.851%   $57.845   $57.85   $57.85   $57.80  
  Purchase #6 $89.77   5.319%   $94.5449   $94.54   $94.55   $94.50  
  Purchase #7 $101.67   11.275%   $113.1333   $113.13   $113.15   $113.10  
  7 purchase totals = $512.04       $550.7204   $550.71   $550.75   $550.50