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 $180.81   13.393%   $205.0259   $205.03   $205.05   $205.00  
  Purchase #2 $207.83   4.740%   $217.6811   $217.68   $217.70   $217.70  
  Purchase #3 $96.29   3.486%   $99.6467   $99.65   $99.65   $99.60  
  Purchase #4 $144.44   10.310%   $159.3318   $159.33   $159.35   $159.30  
  Purchase #5 $224.47   5.184%   $236.1065   $236.11   $236.10   $236.10  
  Purchase #6 $153.31   9.229%   $167.459   $167.46   $167.45   $167.50  
  Purchase #7 $242.38   12.841%   $273.504   $273.50   $273.50   $273.50  
  7 purchase totals = $1,249.53       $1,358.7550   $1,358.76   $1,358.80   $1,358.70