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 $216.75   13.587%   $246.1998   $246.20   $246.20   $246.20  
  Purchase #2 $167.61   5.541%   $176.8973   $176.90   $176.90   $176.90  
  Purchase #3 $87.87   12.537%   $98.8863   $98.89   $98.90   $98.90  
  Purchase #4 $161.94   4.148%   $168.6573   $168.66   $168.65   $168.70  
  Purchase #5 $156.68   12.312%   $175.9704   $175.97   $175.95   $176.00  
  Purchase #6 $70.25   6.542%   $74.8458   $74.85   $74.85   $74.80  
  Purchase #7 $176.69   5.263%   $185.9892   $185.99   $186.00   $186.00  
  7 purchase totals = $1,037.79       $1,127.4461   $1,127.46   $1,127.45   $1,127.50