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 $57.70   9.593%   $63.2352   $63.24   $63.25   $63.20  
  Purchase #2 $106.84   7.337%   $114.6789   $114.68   $114.70   $114.70  
  Purchase #3 $246.46   7.848%   $265.8022   $265.80   $265.80   $265.80  
  Purchase #4 $162.79   9.426%   $178.1346   $178.13   $178.15   $178.10  
  Purchase #5 $67.80   7.613%   $72.9616   $72.96   $72.95   $73.00  
  Purchase #6 $49.55   13.114%   $56.048   $56.05   $56.05   $56.00  
  Purchase #7 $51.82   8.211%   $56.0749   $56.07   $56.05   $56.10  
  7 purchase totals = $742.96       $806.9354   $806.93   $806.95   $806.90