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 $241.44   9.866%   $265.2605   $265.26   $265.25   $265.30  
  Purchase #2 $160.82   3.606%   $166.6192   $166.62   $166.60   $166.60  
  Purchase #3 $213.70   10.240%   $235.5829   $235.58   $235.60   $235.60  
  Purchase #4 $92.49   7.670%   $99.584   $99.58   $99.60   $99.60  
  Purchase #5 $226.81   3.258%   $234.1995   $234.20   $234.20   $234.20  
  Purchase #6 $6.61   4.315%   $6.8952   $6.90   $6.90   $6.90  
  Purchase #7 $165.45   3.364%   $171.0157   $171.02   $171.00   $171.00  
  7 purchase totals = $1,107.32       $1,179.1570   $1,179.16   $1,179.15   $1,179.20