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 $231.38   13.532%   $262.6903   $262.69   $262.70   $262.70  
  Purchase #2 $41.80   4.523%   $43.6906   $43.69   $43.70   $43.70  
  Purchase #3 $134.37   9.230%   $146.7724   $146.77   $146.75   $146.80  
  Purchase #4 $58.67   8.412%   $63.6053   $63.61   $63.60   $63.60  
  Purchase #5 $115.52   13.242%   $130.8172   $130.82   $130.80   $130.80  
  Purchase #6 $6.67   4.198%   $6.95   $6.95   $6.95   $7.00  
  Purchase #7 $86.67   13.440%   $98.3184   $98.32   $98.30   $98.30  
  7 purchase totals = $675.08       $752.8442   $752.85   $752.80   $752.90