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 $19.35   5.339%   $20.3831   $20.38   $20.40   $20.40  
  Purchase #2 $221.43   12.324%   $248.719   $248.72   $248.70   $248.70  
  Purchase #3 $221.95   13.697%   $252.3505   $252.35   $252.35   $252.40  
  Purchase #4 $20.80   3.451%   $21.5178   $21.52   $21.50   $21.50  
  Purchase #5 $208.48   8.142%   $225.4544   $225.45   $225.45   $225.50  
  Purchase #6 $205.85   5.614%   $217.4064   $217.41   $217.40   $217.40  
  Purchase #7 $232.26   11.113%   $258.0711   $258.07   $258.05   $258.10  
  7 purchase totals = $1,130.12       $1,243.9023   $1,243.90   $1,243.85   $1,244.00