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 $245.66   8.797%   $267.2707   $267.27   $267.25   $267.30  
  Purchase #2 $188.49   11.831%   $210.7903   $210.79   $210.80   $210.80  
  Purchase #3 $164.45   13.215%   $186.1821   $186.18   $186.20   $186.20  
  Purchase #4 $219.66   8.683%   $238.7331   $238.73   $238.75   $238.70  
  Purchase #5 $114.63   7.340%   $123.0438   $123.04   $123.05   $123.00  
  Purchase #6 $16.34   3.638%   $16.9344   $16.93   $16.95   $16.90  
  Purchase #7 $192.54   8.688%   $209.2679   $209.27   $209.25   $209.30  
  7 purchase totals = $1,141.77       $1,252.2223   $1,252.21   $1,252.25   $1,252.20