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 $57.92   9.226%   $63.2637   $63.26   $63.25   $63.30  
  Purchase #2 $178.74   7.838%   $192.7496   $192.75   $192.75   $192.70  
  Purchase #3 $207.59   10.508%   $229.4036   $229.40   $229.40   $229.40  
  Purchase #4 $158.91   7.437%   $170.7281   $170.73   $170.75   $170.70  
  Purchase #5 $217.73   9.691%   $238.8302   $238.83   $238.85   $238.80  
  Purchase #6 $174.36   4.862%   $182.8374   $182.84   $182.85   $182.80  
  Purchase #7 $80.34   3.277%   $82.9727   $82.97   $82.95   $83.00  
  7 purchase totals = $1,075.59       $1,160.7853   $1,160.78   $1,160.80   $1,160.70