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 $118.41   13.789%   $134.7376   $134.74   $134.75   $134.70  
  Purchase #2 $149.91   8.593%   $162.7918   $162.79   $162.80   $162.80  
  Purchase #3 $21.49   11.359%   $23.931   $23.93   $23.95   $23.90  
  Purchase #4 $237.48   10.788%   $263.0993   $263.10   $263.10   $263.10  
  Purchase #5 $176.30   5.149%   $185.3777   $185.38   $185.40   $185.40  
  Purchase #6 $18.28   5.335%   $19.2552   $19.26   $19.25   $19.30  
  Purchase #7 $203.87   8.304%   $220.7994   $220.80   $220.80   $220.80  
  7 purchase totals = $925.74       $1,009.9920   $1,010.00   $1,010.05   $1,010.00