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 $42.27   10.113%   $46.5448   $46.54   $46.55   $46.50  
  Purchase #2 $90.60   12.322%   $101.7637   $101.76   $101.75   $101.80  
  Purchase #3 $110.55   6.323%   $117.5401   $117.54   $117.55   $117.50  
  Purchase #4 $41.32   13.809%   $47.0259   $47.03   $47.05   $47.00  
  Purchase #5 $57.83   13.822%   $65.8233   $65.82   $65.80   $65.80  
  Purchase #6 $212.30   10.850%   $235.3346   $235.33   $235.35   $235.30  
  Purchase #7 $168.81   8.189%   $182.6339   $182.63   $182.65   $182.60  
  7 purchase totals = $723.68       $796.6663   $796.65   $796.70   $796.50