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 $46.63   9.278%   $50.9563   $50.96   $50.95   $51.00  
  Purchase #2 $61.72   6.585%   $65.7843   $65.78   $65.80   $65.80  
  Purchase #3 $120.55   7.338%   $129.396   $129.40   $129.40   $129.40  
  Purchase #4 $182.77   3.704%   $189.5398   $189.54   $189.55   $189.50  
  Purchase #5 $176.33   4.753%   $184.711   $184.71   $184.70   $184.70  
  Purchase #6 $250.68   7.619%   $269.7793   $269.78   $269.80   $269.80  
  Purchase #7 $90.49   5.281%   $95.2688   $95.27   $95.25   $95.30  
  7 purchase totals = $929.17       $985.4355   $985.44   $985.45   $985.50