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 $194.91   8.379%   $211.2415   $211.24   $211.25   $211.20  
  Purchase #2 $23.77   10.697%   $26.3127   $26.31   $26.30   $26.30  
  Purchase #3 $98.41   13.366%   $111.5635   $111.56   $111.55   $111.60  
  Purchase #4 $176.58   10.518%   $195.1527   $195.15   $195.15   $195.20  
  Purchase #5 $15.39   7.252%   $16.5061   $16.51   $16.50   $16.50  
  Purchase #6 $112.46   10.770%   $124.5719   $124.57   $124.55   $124.60  
  Purchase #7 $236.94   10.653%   $262.1812   $262.18   $262.20   $262.20  
  7 purchase totals = $858.46       $947.5296   $947.52   $947.50   $947.60