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 $205.73   13.115%   $232.7115   $232.71   $232.70   $232.70  
  Purchase #2 $241.43   13.358%   $273.6802   $273.68   $273.70   $273.70  
  Purchase #3 $247.50   11.212%   $275.2497   $275.25   $275.25   $275.20  
  Purchase #4 $86.41   12.221%   $96.9702   $96.97   $96.95   $97.00  
  Purchase #5 $116.29   9.808%   $127.6957   $127.70   $127.70   $127.70  
  Purchase #6 $14.42   11.106%   $16.0215   $16.02   $16.00   $16.00  
  Purchase #7 $30.37   9.195%   $33.1625   $33.16   $33.15   $33.20  
  7 purchase totals = $942.15       $1,055.4913   $1,055.49   $1,055.45   $1,055.50