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 $189.29   8.487%   $205.355   $205.36   $205.35   $205.40  
  Purchase #2 $84.84   13.861%   $96.5997   $96.60   $96.60   $96.60  
  Purchase #3 $75.48   3.294%   $77.9663   $77.97   $77.95   $78.00  
  Purchase #4 $100.58   3.104%   $103.702   $103.70   $103.70   $103.70  
  Purchase #5 $128.43   8.821%   $139.7588   $139.76   $139.75   $139.80  
  Purchase #6 $105.41   5.807%   $111.5312   $111.53   $111.55   $111.50  
  Purchase #7 $200.74   11.821%   $224.4695   $224.47   $224.45   $224.50  
  7 purchase totals = $884.77       $959.3825   $959.39   $959.35   $959.50