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 $214.65   6.268%   $228.1043   $228.10   $228.10   $228.10  
  Purchase #2 $55.94   9.461%   $61.2325   $61.23   $61.25   $61.20  
  Purchase #3 $118.44   13.716%   $134.6852   $134.69   $134.70   $134.70  
  Purchase #4 $121.55   9.551%   $133.1592   $133.16   $133.15   $133.20  
  Purchase #5 $147.40   3.458%   $152.4971   $152.50   $152.50   $152.50  
  Purchase #6 $146.26   8.730%   $159.0285   $159.03   $159.05   $159.00  
  Purchase #7 $50.99   12.386%   $57.3056   $57.31   $57.30   $57.30  
  7 purchase totals = $855.23       $926.0124   $926.02   $926.05   $926.00