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 $141.54   11.239%   $157.4477   $157.45   $157.45   $157.40  
  Purchase #2 $192.85   13.473%   $218.8327   $218.83   $218.85   $218.80  
  Purchase #3 $190.52   8.426%   $206.5732   $206.57   $206.55   $206.60  
  Purchase #4 $35.64   7.597%   $38.3476   $38.35   $38.35   $38.30  
  Purchase #5 $69.71   11.294%   $77.583   $77.58   $77.60   $77.60  
  Purchase #6 $205.77   4.257%   $214.5296   $214.53   $214.55   $214.50  
  Purchase #7 $48.30   7.468%   $51.907   $51.91   $51.90   $51.90  
  7 purchase totals = $884.33       $965.2208   $965.22   $965.25   $965.10