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 $60.28   3.744%   $62.5369   $62.54   $62.55   $62.50  
  Purchase #2 $51.56   3.498%   $53.3636   $53.36   $53.35   $53.40  
  Purchase #3 $72.46   10.428%   $80.0161   $80.02   $80.00   $80.00  
  Purchase #4 $12.50   6.537%   $13.3171   $13.32   $13.30   $13.30  
  Purchase #5 $212.69   7.474%   $228.5865   $228.59   $228.60   $228.60  
  Purchase #6 $220.76   12.599%   $248.5736   $248.57   $248.55   $248.60  
  Purchase #7 $86.92   12.280%   $97.5938   $97.59   $97.60   $97.60  
  7 purchase totals = $717.17       $783.9876   $783.99   $783.95   $784.00