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 $22.30   11.823%   $24.9365   $24.94   $24.95   $24.90  
  Purchase #2 $157.99   3.274%   $163.1626   $163.16   $163.15   $163.20  
  Purchase #3 $220.64   9.478%   $241.5523   $241.55   $241.55   $241.60  
  Purchase #4 $20.43   5.842%   $21.6235   $21.62   $21.60   $21.60  
  Purchase #5 $222.64   6.193%   $236.4281   $236.43   $236.45   $236.40  
  Purchase #6 $214.88   6.102%   $227.992   $227.99   $228.00   $228.00  
  Purchase #7 $227.53   4.818%   $238.4924   $238.49   $238.50   $238.50  
  7 purchase totals = $1,086.41       $1,154.1874   $1,154.18   $1,154.20   $1,154.20