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 $100.55   8.373%   $108.9691   $108.97   $108.95   $109.00  
  Purchase #2 $121.33   10.825%   $134.464   $134.46   $134.45   $134.50  
  Purchase #3 $122.36   4.412%   $127.7585   $127.76   $127.75   $127.80  
  Purchase #4 $92.94   12.225%   $104.3019   $104.30   $104.30   $104.30  
  Purchase #5 $47.61   9.670%   $52.2139   $52.21   $52.20   $52.20  
  Purchase #6 $94.45   5.756%   $99.8865   $99.89   $99.90   $99.90  
  Purchase #7 $246.80   12.739%   $278.2399   $278.24   $278.25   $278.20  
  7 purchase totals = $826.04       $905.8338   $905.83   $905.80   $905.90