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 $142.26   8.642%   $154.5541   $154.55   $154.55   $154.60  
  Purchase #2 $64.36   8.692%   $69.9542   $69.95   $69.95   $70.00  
  Purchase #3 $205.44   10.743%   $227.5104   $227.51   $227.50   $227.50  
  Purchase #4 $240.83   13.865%   $274.2211   $274.22   $274.20   $274.20  
  Purchase #5 $56.83   7.309%   $60.9837   $60.98   $61.00   $61.00  
  Purchase #6 $185.34   12.484%   $208.4778   $208.48   $208.50   $208.50  
  Purchase #7 $43.84   8.688%   $47.6488   $47.65   $47.65   $47.60  
  7 purchase totals = $938.90       $1,043.3501   $1,043.34   $1,043.35   $1,043.40