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 $60.57   10.416%   $66.879   $66.88   $66.90   $66.90  
  Purchase #2 $167.87   5.820%   $177.64   $177.64   $177.65   $177.60  
  Purchase #3 $201.86   11.120%   $224.3068   $224.31   $224.30   $224.30  
  Purchase #4 $123.77   3.184%   $127.7108   $127.71   $127.70   $127.70  
  Purchase #5 $149.33   3.242%   $154.1713   $154.17   $154.15   $154.20  
  Purchase #6 $13.80   13.234%   $15.6263   $15.63   $15.65   $15.60  
  Purchase #7 $20.25   5.372%   $21.3378   $21.34   $21.35   $21.30  
  7 purchase totals = $737.45       $787.6720   $787.68   $787.70   $787.60