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 $69.62   11.441%   $77.5852   $77.59   $77.60   $77.60  
  Purchase #2 $72.86   11.664%   $81.3584   $81.36   $81.35   $81.40  
  Purchase #3 $129.62   3.309%   $133.9091   $133.91   $133.90   $133.90  
  Purchase #4 $73.28   3.544%   $75.877   $75.88   $75.90   $75.90  
  Purchase #5 $167.91   9.448%   $183.7741   $183.77   $183.75   $183.80  
  Purchase #6 $177.39   4.131%   $184.718   $184.72   $184.70   $184.70  
  Purchase #7 $199.46   11.557%   $222.5116   $222.51   $222.50   $222.50  
  7 purchase totals = $890.14       $959.7334   $959.74   $959.70   $959.80