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 $211.35   7.282%   $226.7405   $226.74   $226.75   $226.70  
  Purchase #2 $105.87   5.449%   $111.6389   $111.64   $111.65   $111.60  
  Purchase #3 $125.40   4.724%   $131.3239   $131.32   $131.30   $131.30  
  Purchase #4 $105.94   9.178%   $115.6632   $115.66   $115.65   $115.70  
  Purchase #5 $114.63   8.517%   $124.393   $124.39   $124.40   $124.40  
  Purchase #6 $68.52   13.635%   $77.8627   $77.86   $77.85   $77.90  
  Purchase #7 $153.55   13.726%   $174.6263   $174.63   $174.65   $174.60  
  7 purchase totals = $885.26       $962.2485   $962.24   $962.25   $962.20