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 $75.87   13.830%   $86.3628   $86.36   $86.35   $86.40  
  Purchase #2 $230.30   12.478%   $259.0368   $259.04   $259.05   $259.00  
  Purchase #3 $47.25   13.344%   $53.555   $53.56   $53.55   $53.60  
  Purchase #4 $157.73   3.508%   $163.2632   $163.26   $163.25   $163.30  
  Purchase #5 $100.46   10.120%   $110.6266   $110.63   $110.65   $110.60  
  Purchase #6 $241.26   9.381%   $263.8926   $263.89   $263.90   $263.90  
  Purchase #7 $26.30   12.826%   $29.6732   $29.67   $29.65   $29.70  
  7 purchase totals = $879.17       $966.4102   $966.41   $966.40   $966.50