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 $62.35   6.763%   $66.5667   $66.57   $66.55   $66.60  
  Purchase #2 $236.52   12.574%   $266.26   $266.26   $266.25   $266.30  
  Purchase #3 $47.52   3.172%   $49.0273   $49.03   $49.05   $49.00  
  Purchase #4 $201.41   5.712%   $212.9145   $212.91   $212.90   $212.90  
  Purchase #5 $235.50   10.321%   $259.806   $259.81   $259.80   $259.80  
  Purchase #6 $19.76   8.219%   $21.3841   $21.38   $21.40   $21.40  
  Purchase #7 $152.73   3.169%   $157.57   $157.57   $157.55   $157.60  
  7 purchase totals = $955.79       $1,033.5286   $1,033.53   $1,033.50   $1,033.60