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 $212.35   13.848%   $241.7562   $241.76   $241.75   $241.80  
  Purchase #2 $250.65   6.301%   $266.4435   $266.44   $266.45   $266.40  
  Purchase #3 $71.48   3.335%   $73.8639   $73.86   $73.85   $73.90  
  Purchase #4 $218.34   4.531%   $228.233   $228.23   $228.25   $228.20  
  Purchase #5 $226.88   9.741%   $248.9804   $248.98   $249.00   $249.00  
  Purchase #6 $87.35   13.693%   $99.3108   $99.31   $99.30   $99.30  
  Purchase #7 $73.94   12.767%   $83.3799   $83.38   $83.40   $83.40  
  7 purchase totals = $1,140.99       $1,241.9677   $1,241.96   $1,242.00   $1,242.00