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 $242.38   4.362%   $252.9526   $252.95   $252.95   $253.00  
  Purchase #2 $41.42   12.159%   $46.4563   $46.46   $46.45   $46.50  
  Purchase #3 $148.59   4.381%   $155.0997   $155.10   $155.10   $155.10  
  Purchase #4 $123.47   6.296%   $131.2437   $131.24   $131.25   $131.20  
  Purchase #5 $51.86   11.237%   $57.6875   $57.69   $57.70   $57.70  
  Purchase #6 $96.85   4.485%   $101.1937   $101.19   $101.20   $101.20  
  Purchase #7 $44.70   9.391%   $48.8978   $48.90   $48.90   $48.90  
  7 purchase totals = $749.27       $793.5313   $793.53   $793.55   $793.60