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 $241.43   11.684%   $269.6387   $269.64   $269.65   $269.60  
  Purchase #2 $150.72   5.209%   $158.571   $158.57   $158.55   $158.60  
  Purchase #3 $17.71   12.646%   $19.9496   $19.95   $19.95   $19.90  
  Purchase #4 $248.40   7.310%   $266.558   $266.56   $266.55   $266.60  
  Purchase #5 $92.47   3.476%   $95.6843   $95.68   $95.70   $95.70  
  Purchase #6 $114.66   8.445%   $124.343   $124.34   $124.35   $124.30  
  Purchase #7 $114.50   3.485%   $118.4903   $118.49   $118.50   $118.50  
  7 purchase totals = $979.89       $1,053.2349   $1,053.23   $1,053.25   $1,053.20