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 $232.73   12.696%   $262.2774   $262.28   $262.30   $262.30  
  Purchase #2 $207.31   8.393%   $224.7095   $224.71   $224.70   $224.70  
  Purchase #3 $214.84   12.159%   $240.9624   $240.96   $240.95   $241.00  
  Purchase #4 $46.29   10.237%   $51.0287   $51.03   $51.05   $51.00  
  Purchase #5 $201.87   13.331%   $228.7813   $228.78   $228.80   $228.80  
  Purchase #6 $191.83   9.558%   $210.1651   $210.17   $210.15   $210.20  
  Purchase #7 $10.71   3.281%   $11.0614   $11.06   $11.05   $11.10  
  7 purchase totals = $1,105.58       $1,228.9858   $1,228.99   $1,229.00   $1,229.10