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 $116.88   11.381%   $130.1821   $130.18   $130.20   $130.20  
  Purchase #2 $217.88   10.823%   $241.4612   $241.46   $241.45   $241.50  
  Purchase #3 $198.55   4.136%   $206.762   $206.76   $206.75   $206.80  
  Purchase #4 $246.90   7.658%   $265.8076   $265.81   $265.80   $265.80  
  Purchase #5 $105.92   7.760%   $114.1394   $114.14   $114.15   $114.10  
  Purchase #6 $75.93   4.817%   $79.5875   $79.59   $79.60   $79.60  
  Purchase #7 $8.65   11.151%   $9.6146   $9.61   $9.60   $9.60  
  7 purchase totals = $970.71       $1,047.5544   $1,047.55   $1,047.55   $1,047.60