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 $241.54   11.758%   $269.9403   $269.94   $269.95   $269.90  
  Purchase #2 $244.60   6.123%   $259.5769   $259.58   $259.60   $259.60  
  Purchase #3 $238.65   8.460%   $258.8398   $258.84   $258.85   $258.80  
  Purchase #4 $101.87   11.672%   $113.7603   $113.76   $113.75   $113.80  
  Purchase #5 $231.75   11.419%   $258.2135   $258.21   $258.20   $258.20  
  Purchase #6 $181.35   5.437%   $191.21   $191.21   $191.20   $191.20  
  Purchase #7 $194.83   7.112%   $208.6863   $208.69   $208.70   $208.70  
  7 purchase totals = $1,434.59       $1,560.2271   $1,560.23   $1,560.25   $1,560.20