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 $235.73   13.624%   $267.8459   $267.85   $267.85   $267.80  
  Purchase #2 $34.61   12.499%   $38.9359   $38.94   $38.95   $38.90  
  Purchase #3 $243.36   9.188%   $265.7199   $265.72   $265.70   $265.70  
  Purchase #4 $216.70   4.504%   $226.4602   $226.46   $226.45   $226.50  
  Purchase #5 $82.76   11.414%   $92.2062   $92.21   $92.20   $92.20  
  Purchase #6 $34.87   9.646%   $38.2336   $38.23   $38.25   $38.20  
  Purchase #7 $58.99   6.207%   $62.6515   $62.65   $62.65   $62.70  
  7 purchase totals = $907.02       $992.0532   $992.06   $992.05   $992.00