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 $216.86   8.640%   $235.5967   $235.60   $235.60   $235.60  
  Purchase #2 $51.87   9.113%   $56.5969   $56.60   $56.60   $56.60  
  Purchase #3 $193.27   5.420%   $203.7452   $203.75   $203.75   $203.70  
  Purchase #4 $221.89   12.403%   $249.411   $249.41   $249.40   $249.40  
  Purchase #5 $136.72   12.589%   $153.9317   $153.93   $153.95   $153.90  
  Purchase #6 $129.95   4.748%   $136.12   $136.12   $136.10   $136.10  
  Purchase #7 $211.60   8.828%   $230.28   $230.28   $230.30   $230.30  
  7 purchase totals = $1,162.16       $1,265.6815   $1,265.69   $1,265.70   $1,265.60