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 $189.62   9.255%   $207.1693   $207.17   $207.15   $207.20  
  Purchase #2 $126.81   10.533%   $140.1669   $140.17   $140.15   $140.20  
  Purchase #3 $186.76   5.296%   $196.6508   $196.65   $196.65   $196.70  
  Purchase #4 $68.96   4.826%   $72.288   $72.29   $72.30   $72.30  
  Purchase #5 $49.44   12.722%   $55.7298   $55.73   $55.75   $55.70  
  Purchase #6 $132.54   3.343%   $136.9708   $136.97   $136.95   $137.00  
  Purchase #7 $175.80   6.257%   $186.7998   $186.80   $186.80   $186.80  
  7 purchase totals = $929.93       $995.7754   $995.78   $995.75   $995.90