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 $96.85   13.724%   $110.1417   $110.14   $110.15   $110.10  
  Purchase #2 $157.84   11.293%   $175.6649   $175.66   $175.65   $175.70  
  Purchase #3 $218.99   3.797%   $227.3051   $227.31   $227.30   $227.30  
  Purchase #4 $134.53   4.470%   $140.5435   $140.54   $140.55   $140.50  
  Purchase #5 $217.51   4.862%   $228.0853   $228.09   $228.10   $228.10  
  Purchase #6 $191.98   3.252%   $198.2232   $198.22   $198.20   $198.20  
  Purchase #7 $127.97   11.232%   $142.3436   $142.34   $142.35   $142.30  
  7 purchase totals = $1,145.67       $1,222.3073   $1,222.30   $1,222.30   $1,222.20