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 $228.80   9.624%   $250.8197   $250.82   $250.80   $250.80  
  Purchase #2 $65.54   12.216%   $73.5464   $73.55   $73.55   $73.50  
  Purchase #3 $85.37   12.638%   $96.1591   $96.16   $96.15   $96.20  
  Purchase #4 $58.59   7.530%   $63.0018   $63.00   $63.00   $63.00  
  Purchase #5 $80.61   12.419%   $90.621   $90.62   $90.60   $90.60  
  Purchase #6 $168.57   10.858%   $186.8733   $186.87   $186.85   $186.90  
  Purchase #7 $215.94   9.650%   $236.7782   $236.78   $236.80   $236.80  
  7 purchase totals = $903.42       $997.7995   $997.80   $997.75   $997.80