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 $241.48   3.640%   $250.2699   $250.27   $250.25   $250.30  
  Purchase #2 $70.54   3.538%   $73.0357   $73.04   $73.05   $73.00  
  Purchase #3 $58.28   7.688%   $62.7606   $62.76   $62.75   $62.80  
  Purchase #4 $119.62   5.430%   $126.1154   $126.12   $126.10   $126.10  
  Purchase #5 $217.30   6.789%   $232.0525   $232.05   $232.05   $232.10  
  Purchase #6 $69.91   8.711%   $75.9999   $76.00   $76.00   $76.00  
  Purchase #7 $146.74   5.589%   $154.9413   $154.94   $154.95   $154.90  
  7 purchase totals = $923.87       $975.1753   $975.18   $975.15   $975.20