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 $96.26   11.734%   $107.5551   $107.56   $107.55   $107.60  
  Purchase #2 $57.33   9.438%   $62.7408   $62.74   $62.75   $62.70  
  Purchase #3 $107.80   6.252%   $114.5397   $114.54   $114.55   $114.50  
  Purchase #4 $6.91   11.674%   $7.7167   $7.72   $7.70   $7.70  
  Purchase #5 $107.66   8.608%   $116.9274   $116.93   $116.95   $116.90  
  Purchase #6 $244.35   8.500%   $265.1198   $265.12   $265.10   $265.10  
  Purchase #7 $47.99   8.153%   $51.9026   $51.90   $51.90   $51.90  
  7 purchase totals = $668.30       $726.5021   $726.51   $726.50   $726.40