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 $208.76   13.772%   $237.5104   $237.51   $237.50   $237.50  
  Purchase #2 $73.51   9.552%   $80.5317   $80.53   $80.55   $80.50  
  Purchase #3 $86.92   5.404%   $91.6172   $91.62   $91.60   $91.60  
  Purchase #4 $221.92   11.744%   $247.9823   $247.98   $248.00   $248.00  
  Purchase #5 $131.84   8.693%   $143.3009   $143.30   $143.30   $143.30  
  Purchase #6 $205.51   9.248%   $224.5156   $224.52   $224.50   $224.50  
  Purchase #7 $50.61   10.730%   $56.0405   $56.04   $56.05   $56.00  
  7 purchase totals = $979.07       $1,081.4986   $1,081.50   $1,081.50   $1,081.40