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 $32.81   11.481%   $36.5769   $36.58   $36.60   $36.60  
  Purchase #2 $112.97   10.216%   $124.511   $124.51   $124.50   $124.50  
  Purchase #3 $167.99   3.835%   $174.4324   $174.43   $174.45   $174.40  
  Purchase #4 $201.41   3.686%   $208.834   $208.83   $208.85   $208.80  
  Purchase #5 $73.39   4.313%   $76.5553   $76.56   $76.55   $76.60  
  Purchase #6 $55.50   10.554%   $61.3575   $61.36   $61.35   $61.40  
  Purchase #7 $117.71   6.520%   $125.3847   $125.38   $125.40   $125.40  
  7 purchase totals = $761.78       $807.6518   $807.65   $807.70   $807.70