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 $53.79   13.676%   $61.1463   $61.15   $61.15   $61.10  
  Purchase #2 $118.61   11.366%   $132.0912   $132.09   $132.10   $132.10  
  Purchase #3 $25.53   6.312%   $27.1415   $27.14   $27.15   $27.10  
  Purchase #4 $227.81   9.151%   $248.6569   $248.66   $248.65   $248.70  
  Purchase #5 $133.30   13.669%   $151.5208   $151.52   $151.50   $151.50  
  Purchase #6 $163.94   7.245%   $175.8175   $175.82   $175.80   $175.80  
  Purchase #7 $23.72   8.510%   $25.7386   $25.74   $25.75   $25.70  
  7 purchase totals = $746.70       $822.1128   $822.12   $822.10   $822.00