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 $241.77   8.234%   $261.6773   $261.68   $261.70   $261.70  
  Purchase #2 $132.34   5.352%   $139.4228   $139.42   $139.40   $139.40  
  Purchase #3 $22.77   7.224%   $24.4149   $24.41   $24.40   $24.40  
  Purchase #4 $174.69   11.639%   $195.0222   $195.02   $195.00   $195.00  
  Purchase #5 $112.58   10.346%   $124.2275   $124.23   $124.25   $124.20  
  Purchase #6 $38.49   7.728%   $41.4645   $41.46   $41.45   $41.50  
  Purchase #7 $221.61   4.141%   $230.7869   $230.79   $230.80   $230.80  
  7 purchase totals = $944.25       $1,017.0161   $1,017.01   $1,017.00   $1,017.00