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 $98.26   9.500%   $107.5947   $107.59   $107.60   $107.60  
  Purchase #2 $41.97   3.432%   $43.4104   $43.41   $43.40   $43.40  
  Purchase #3 $32.77   8.114%   $35.429   $35.43   $35.45   $35.40  
  Purchase #4 $106.77   9.417%   $116.8245   $116.82   $116.80   $116.80  
  Purchase #5 $76.53   12.802%   $86.3274   $86.33   $86.35   $86.30  
  Purchase #6 $195.31   3.338%   $201.8294   $201.83   $201.85   $201.80  
  Purchase #7 $13.41   10.839%   $14.8635   $14.86   $14.85   $14.90  
  7 purchase totals = $565.02       $606.2789   $606.27   $606.30   $606.20