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 $85.84   12.724%   $96.7623   $96.76   $96.75   $96.80  
  Purchase #2 $195.37   5.650%   $206.4084   $206.41   $206.40   $206.40  
  Purchase #3 $62.53   4.369%   $65.2619   $65.26   $65.25   $65.30  
  Purchase #4 $35.26   9.221%   $38.5113   $38.51   $38.50   $38.50  
  Purchase #5 $114.79   11.462%   $127.9472   $127.95   $127.95   $127.90  
  Purchase #6 $180.99   3.381%   $187.1093   $187.11   $187.10   $187.10  
  Purchase #7 $92.33   12.842%   $104.187   $104.19   $104.20   $104.20  
  7 purchase totals = $767.11       $826.1874   $826.19   $826.15   $826.20