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 $151.83   4.613%   $158.8339   $158.83   $158.85   $158.80  
  Purchase #2 $62.59   10.675%   $69.2715   $69.27   $69.25   $69.30  
  Purchase #3 $129.99   11.477%   $144.909   $144.91   $144.90   $144.90  
  Purchase #4 $239.33   8.780%   $260.3432   $260.34   $260.35   $260.30  
  Purchase #5 $122.58   8.698%   $133.242   $133.24   $133.25   $133.20  
  Purchase #6 $5.45   8.681%   $5.9231   $5.92   $5.90   $5.90  
  Purchase #7 $171.81   3.488%   $177.8027   $177.80   $177.80   $177.80  
  7 purchase totals = $883.58       $950.3254   $950.31   $950.30   $950.20