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 $216.78   11.416%   $241.5276   $241.53   $241.55   $241.50  
  Purchase #2 $121.99   3.574%   $126.3499   $126.35   $126.35   $126.30  
  Purchase #3 $244.59   4.786%   $256.2961   $256.30   $256.30   $256.30  
  Purchase #4 $231.87   9.681%   $254.3173   $254.32   $254.30   $254.30  
  Purchase #5 $166.63   9.736%   $182.8531   $182.85   $182.85   $182.90  
  Purchase #6 $176.96   13.865%   $201.4955   $201.50   $201.50   $201.50  
  Purchase #7 $210.25   8.338%   $227.7806   $227.78   $227.80   $227.80  
  7 purchase totals = $1,369.07       $1,490.6201   $1,490.63   $1,490.65   $1,490.60