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 $215.36   10.623%   $238.2377   $238.24   $238.25   $238.20  
  Purchase #2 $223.31   5.402%   $235.3732   $235.37   $235.35   $235.40  
  Purchase #3 $100.27   5.373%   $105.6575   $105.66   $105.65   $105.70  
  Purchase #4 $77.45   7.243%   $83.0597   $83.06   $83.05   $83.10  
  Purchase #5 $238.56   10.719%   $264.1312   $264.13   $264.15   $264.10  
  Purchase #6 $225.68   3.862%   $234.3958   $234.40   $234.40   $234.40  
  Purchase #7 $119.73   12.662%   $134.8902   $134.89   $134.90   $134.90  
  7 purchase totals = $1,200.36       $1,295.7453   $1,295.75   $1,295.75   $1,295.80