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 $239.44   9.719%   $262.7112   $262.71   $262.70   $262.70  
  Purchase #2 $211.76   8.729%   $230.2445   $230.24   $230.25   $230.20  
  Purchase #3 $37.27   11.299%   $41.4811   $41.48   $41.50   $41.50  
  Purchase #4 $24.42   7.653%   $26.2889   $26.29   $26.30   $26.30  
  Purchase #5 $227.57   6.612%   $242.6169   $242.62   $242.60   $242.60  
  Purchase #6 $233.52   10.771%   $258.6724   $258.67   $258.65   $258.70  
  Purchase #7 $198.48   7.786%   $213.9337   $213.93   $213.95   $213.90  
  7 purchase totals = $1,172.46       $1,275.9487   $1,275.94   $1,275.95   $1,275.90