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 $184.41   4.365%   $192.4595   $192.46   $192.45   $192.50  
  Purchase #2 $94.36   13.704%   $107.2911   $107.29   $107.30   $107.30  
  Purchase #3 $134.61   8.346%   $145.8446   $145.84   $145.85   $145.80  
  Purchase #4 $125.78   11.108%   $139.7516   $139.75   $139.75   $139.80  
  Purchase #5 $234.31   11.363%   $260.9346   $260.93   $260.95   $260.90  
  Purchase #6 $72.79   12.547%   $81.923   $81.92   $81.90   $81.90  
  Purchase #7 $14.69   3.589%   $15.2172   $15.22   $15.20   $15.20  
  7 purchase totals = $860.95       $943.4216   $943.41   $943.40   $943.40