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 $179.88   13.206%   $203.635   $203.64   $203.65   $203.60  
  Purchase #2 $181.27   12.317%   $203.597   $203.60   $203.60   $203.60  
  Purchase #3 $241.76   12.686%   $272.4297   $272.43   $272.45   $272.40  
  Purchase #4 $207.37   13.536%   $235.4396   $235.44   $235.45   $235.40  
  Purchase #5 $134.31   13.572%   $152.5386   $152.54   $152.55   $152.50  
  Purchase #6 $243.59   3.703%   $252.6101   $252.61   $252.60   $252.60  
  Purchase #7 $134.77   10.306%   $148.6594   $148.66   $148.65   $148.70  
  7 purchase totals = $1,322.95       $1,468.9094   $1,468.92   $1,468.95   $1,468.80