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 $226.77   10.653%   $250.9278   $250.93   $250.95   $250.90  
  Purchase #2 $240.76   4.670%   $252.0035   $252.00   $252.00   $252.00  
  Purchase #3 $177.69   3.536%   $183.9731   $183.97   $183.95   $184.00  
  Purchase #4 $82.36   11.119%   $91.5176   $91.52   $91.50   $91.50  
  Purchase #5 $135.87   12.315%   $152.6024   $152.60   $152.60   $152.60  
  Purchase #6 $49.52   5.499%   $52.2431   $52.24   $52.25   $52.20  
  Purchase #7 $48.55   3.509%   $50.2536   $50.25   $50.25   $50.30  
  7 purchase totals = $961.52       $1,033.5211   $1,033.51   $1,033.50   $1,033.50