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 $242.47   8.764%   $263.7201   $263.72   $263.70   $263.70  
  Purchase #2 $142.76   9.801%   $156.7519   $156.75   $156.75   $156.80  
  Purchase #3 $250.84   7.292%   $269.1313   $269.13   $269.15   $269.10  
  Purchase #4 $101.86   10.213%   $112.263   $112.26   $112.25   $112.30  
  Purchase #5 $60.38   6.762%   $64.4629   $64.46   $64.45   $64.50  
  Purchase #6 $70.79   3.800%   $73.48   $73.48   $73.50   $73.50  
  Purchase #7 $200.93   13.506%   $228.0676   $228.07   $228.05   $228.10  
  7 purchase totals = $1,070.03       $1,167.8768   $1,167.87   $1,167.85   $1,168.00