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 $79.44   4.805%   $83.2571   $83.26   $83.25   $83.30  
  Purchase #2 $170.87   13.305%   $193.6043   $193.60   $193.60   $193.60  
  Purchase #3 $62.41   11.863%   $69.8137   $69.81   $69.80   $69.80  
  Purchase #4 $225.44   12.532%   $253.6921   $253.69   $253.70   $253.70  
  Purchase #5 $220.29   12.768%   $248.4166   $248.42   $248.40   $248.40  
  Purchase #6 $36.26   13.696%   $41.2262   $41.23   $41.25   $41.20  
  Purchase #7 $127.93   12.800%   $144.305   $144.31   $144.30   $144.30  
  7 purchase totals = $922.64       $1,034.3150   $1,034.32   $1,034.30   $1,034.30