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 $237.49   11.614%   $265.0721   $265.07   $265.05   $265.10  
  Purchase #2 $16.26   9.565%   $17.8153   $17.82   $17.80   $17.80  
  Purchase #3 $128.98   8.177%   $139.5267   $139.53   $139.55   $139.50  
  Purchase #4 $246.50   10.568%   $272.5501   $272.55   $272.55   $272.60  
  Purchase #5 $107.34   8.414%   $116.3716   $116.37   $116.35   $116.40  
  Purchase #6 $196.68   13.350%   $222.9368   $222.94   $222.95   $222.90  
  Purchase #7 $220.63   3.171%   $227.6262   $227.63   $227.65   $227.60  
  7 purchase totals = $1,153.88       $1,261.8988   $1,261.91   $1,261.90   $1,261.90