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 $130.96   7.867%   $141.2626   $141.26   $141.25   $141.30  
  Purchase #2 $224.95   10.246%   $247.9984   $248.00   $248.00   $248.00  
  Purchase #3 $215.88   7.662%   $232.4207   $232.42   $232.40   $232.40  
  Purchase #4 $158.66   5.534%   $167.4402   $167.44   $167.45   $167.40  
  Purchase #5 $145.32   7.693%   $156.4995   $156.50   $156.50   $156.50  
  Purchase #6 $37.33   4.564%   $39.0337   $39.03   $39.05   $39.00  
  Purchase #7 $10.97   5.576%   $11.5817   $11.58   $11.60   $11.60  
  7 purchase totals = $924.07       $996.2368   $996.23   $996.25   $996.20