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 $163.67   13.756%   $186.1844   $186.18   $186.20   $186.20  
  Purchase #2 $14.88   12.304%   $16.7108   $16.71   $16.70   $16.70  
  Purchase #3 $113.48   8.533%   $123.1632   $123.16   $123.15   $123.20  
  Purchase #4 $189.59   5.733%   $200.4592   $200.46   $200.45   $200.50  
  Purchase #5 $160.91   3.186%   $166.0366   $166.04   $166.05   $166.00  
  Purchase #6 $153.84   10.678%   $170.267   $170.27   $170.25   $170.30  
  Purchase #7 $186.93   7.459%   $200.8731   $200.87   $200.85   $200.90  
  7 purchase totals = $983.30       $1,063.6943   $1,063.69   $1,063.65   $1,063.80