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 $60.67   7.246%   $65.0661   $65.07   $65.05   $65.10  
  Purchase #2 $47.95   4.454%   $50.0857   $50.09   $50.10   $50.10  
  Purchase #3 $245.25   7.153%   $262.7927   $262.79   $262.80   $262.80  
  Purchase #4 $190.91   7.377%   $204.9934   $204.99   $205.00   $205.00  
  Purchase #5 $206.91   8.659%   $224.8263   $224.83   $224.85   $224.80  
  Purchase #6 $119.95   9.544%   $131.398   $131.40   $131.40   $131.40  
  Purchase #7 $34.32   11.256%   $38.1831   $38.18   $38.20   $38.20  
  7 purchase totals = $905.96       $977.3453   $977.35   $977.40   $977.40