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 $235.29   5.502%   $248.2357   $248.24   $248.25   $248.20  
  Purchase #2 $55.30   9.587%   $60.6016   $60.60   $60.60   $60.60  
  Purchase #3 $46.73   4.223%   $48.7034   $48.70   $48.70   $48.70  
  Purchase #4 $98.84   13.722%   $112.4028   $112.40   $112.40   $112.40  
  Purchase #5 $241.90   3.703%   $250.8576   $250.86   $250.85   $250.90  
  Purchase #6 $38.97   4.351%   $40.6656   $40.67   $40.65   $40.70  
  Purchase #7 $41.95   3.770%   $43.5315   $43.53   $43.55   $43.50  
  7 purchase totals = $758.98       $804.9982   $805.00   $805.00   $805.00