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 $66.65   9.794%   $73.1777   $73.18   $73.20   $73.20  
  Purchase #2 $247.75   3.491%   $256.399   $256.40   $256.40   $256.40  
  Purchase #3 $68.67   5.336%   $72.3342   $72.33   $72.35   $72.30  
  Purchase #4 $49.47   9.704%   $54.2706   $54.27   $54.25   $54.30  
  Purchase #5 $114.41   7.804%   $123.3386   $123.34   $123.35   $123.30  
  Purchase #6 $175.55   10.255%   $193.5527   $193.55   $193.55   $193.60  
  Purchase #7 $16.50   12.865%   $18.6227   $18.62   $18.60   $18.60  
  7 purchase totals = $739.00       $791.6955   $791.69   $791.70   $791.70