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 $102.65   13.583%   $116.5929   $116.59   $116.60   $116.60  
  Purchase #2 $189.50   7.124%   $203   $203.00   $203.00   $203.00  
  Purchase #3 $135.95   12.162%   $152.4842   $152.48   $152.50   $152.50  
  Purchase #4 $243.36   7.373%   $261.3029   $261.30   $261.30   $261.30  
  Purchase #5 $179.87   6.364%   $191.3169   $191.32   $191.30   $191.30  
  Purchase #6 $133.67   5.784%   $141.4015   $141.40   $141.40   $141.40  
  Purchase #7 $186.69   4.547%   $195.1788   $195.18   $195.20   $195.20  
  7 purchase totals = $1,171.69       $1,261.2772   $1,261.27   $1,261.30   $1,261.30