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 $160.71   10.293%   $177.2519   $177.25   $177.25   $177.30  
  Purchase #2 $55.70   3.643%   $57.7292   $57.73   $57.75   $57.70  
  Purchase #3 $181.81   12.821%   $205.1199   $205.12   $205.10   $205.10  
  Purchase #4 $88.39   7.735%   $95.227   $95.23   $95.25   $95.20  
  Purchase #5 $40.30   9.540%   $44.1446   $44.14   $44.15   $44.10  
  Purchase #6 $102.45   11.266%   $113.992   $113.99   $114.00   $114.00  
  Purchase #7 $204.87   6.220%   $217.6129   $217.61   $217.60   $217.60  
  7 purchase totals = $834.23       $911.0775   $911.07   $911.10   $911.00