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 $58.84   4.828%   $61.6808   $61.68   $61.70   $61.70  
  Purchase #2 $68.63   12.666%   $77.3227   $77.32   $77.30   $77.30  
  Purchase #3 $215.62   3.676%   $223.5462   $223.55   $223.55   $223.50  
  Purchase #4 $27.38   6.309%   $29.1074   $29.11   $29.10   $29.10  
  Purchase #5 $156.65   4.605%   $163.8637   $163.86   $163.85   $163.90  
  Purchase #6 $148.41   5.633%   $156.7699   $156.77   $156.75   $156.80  
  Purchase #7 $60.63   9.150%   $66.1776   $66.18   $66.20   $66.20  
  7 purchase totals = $736.16       $778.4683   $778.47   $778.45   $778.50