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 $118.66   6.826%   $126.7597   $126.76   $126.75   $126.80  
  Purchase #2 $73.74   4.167%   $76.8127   $76.81   $76.80   $76.80  
  Purchase #3 $141.48   6.735%   $151.0087   $151.01   $151.00   $151.00  
  Purchase #4 $35.74   13.431%   $40.5402   $40.54   $40.55   $40.50  
  Purchase #5 $241.74   10.132%   $266.2331   $266.23   $266.25   $266.20  
  Purchase #6 $106.87   8.458%   $115.9091   $115.91   $115.90   $115.90  
  Purchase #7 $217.52   3.324%   $224.7504   $224.75   $224.75   $224.80  
  7 purchase totals = $935.75       $1,002.0139   $1,002.01   $1,002.00   $1,002.00