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 $243.26   10.694%   $269.2742   $269.27   $269.25   $269.30  
  Purchase #2 $150.92   6.767%   $161.1328   $161.13   $161.15   $161.10  
  Purchase #3 $133.31   3.541%   $138.0305   $138.03   $138.05   $138.00  
  Purchase #4 $189.76   13.327%   $215.0493   $215.05   $215.05   $215.00  
  Purchase #5 $119.31   11.226%   $132.7037   $132.70   $132.70   $132.70  
  Purchase #6 $160.77   4.152%   $167.4452   $167.45   $167.45   $167.40  
  Purchase #7 $108.97   5.477%   $114.9383   $114.94   $114.95   $114.90  
  7 purchase totals = $1,106.30       $1,198.5740   $1,198.57   $1,198.60   $1,198.40