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 $226.62   10.321%   $250.0095   $250.01   $250.00   $250.00  
  Purchase #2 $163.86   12.689%   $184.6522   $184.65   $184.65   $184.70  
  Purchase #3 $45.85   8.564%   $49.7766   $49.78   $49.80   $49.80  
  Purchase #4 $233.42   3.855%   $242.4183   $242.42   $242.40   $242.40  
  Purchase #5 $43.32   6.557%   $46.1605   $46.16   $46.15   $46.20  
  Purchase #6 $194.80   11.135%   $216.491   $216.49   $216.50   $216.50  
  Purchase #7 $216.64   6.109%   $229.8745   $229.87   $229.85   $229.90  
  7 purchase totals = $1,124.51       $1,219.3826   $1,219.38   $1,219.35   $1,219.50