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 $206.95   9.218%   $226.0267   $226.03   $226.05   $226.00  
  Purchase #2 $27.54   3.334%   $28.4582   $28.46   $28.45   $28.50  
  Purchase #3 $36.29   5.757%   $38.3792   $38.38   $38.40   $38.40  
  Purchase #4 $184.76   3.733%   $191.6571   $191.66   $191.65   $191.70  
  Purchase #5 $111.82   7.133%   $119.7961   $119.80   $119.80   $119.80  
  Purchase #6 $111.42   13.713%   $126.699   $126.70   $126.70   $126.70  
  Purchase #7 $217.89   6.408%   $231.8524   $231.85   $231.85   $231.90  
  7 purchase totals = $896.67       $962.8687   $962.88   $962.90   $963.00