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 $188.35   8.460%   $204.2844   $204.28   $204.30   $204.30  
  Purchase #2 $142.41   4.594%   $148.9523   $148.95   $148.95   $149.00  
  Purchase #3 $21.60   8.686%   $23.4762   $23.48   $23.50   $23.50  
  Purchase #4 $82.27   5.737%   $86.9898   $86.99   $87.00   $87.00  
  Purchase #5 $248.33   8.448%   $269.3089   $269.31   $269.30   $269.30  
  Purchase #6 $28.69   7.272%   $30.7763   $30.78   $30.80   $30.80  
  Purchase #7 $177.42   3.655%   $183.9047   $183.90   $183.90   $183.90  
  7 purchase totals = $889.07       $947.6926   $947.69   $947.75   $947.80