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 $224.47   3.158%   $231.5588   $231.56   $231.55   $231.60  
  Purchase #2 $162.66   13.255%   $184.2206   $184.22   $184.20   $184.20  
  Purchase #3 $224.27   6.359%   $238.5313   $238.53   $238.55   $238.50  
  Purchase #4 $23.95   3.190%   $24.714   $24.71   $24.70   $24.70  
  Purchase #5 $190.41   6.402%   $202.6   $202.60   $202.60   $202.60  
  Purchase #6 $207.46   10.400%   $229.0358   $229.04   $229.05   $229.00  
  Purchase #7 $171.31   12.675%   $193.0235   $193.02   $193.00   $193.00  
  7 purchase totals = $1,204.53       $1,303.6840   $1,303.68   $1,303.65   $1,303.60