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 $153.37   6.605%   $163.5001   $163.50   $163.50   $163.50  
  Purchase #2 $243.29   7.641%   $261.8798   $261.88   $261.90   $261.90  
  Purchase #3 $205.57   7.810%   $221.625   $221.63   $221.65   $221.60  
  Purchase #4 $63.64   7.291%   $68.28   $68.28   $68.30   $68.30  
  Purchase #5 $69.99   5.737%   $74.0053   $74.01   $74.00   $74.00  
  Purchase #6 $162.67   12.553%   $183.09   $183.09   $183.10   $183.10  
  Purchase #7 $117.44   11.280%   $130.6872   $130.69   $130.70   $130.70  
  7 purchase totals = $1,015.97       $1,103.0674   $1,103.08   $1,103.15   $1,103.10