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 $188.99   8.749%   $205.5247   $205.52   $205.50   $205.50  
  Purchase #2 $191.45   13.670%   $217.6212   $217.62   $217.60   $217.60  
  Purchase #3 $207.61   9.414%   $227.1544   $227.15   $227.15   $227.20  
  Purchase #4 $12.81   11.316%   $14.2596   $14.26   $14.25   $14.30  
  Purchase #5 $37.46   10.591%   $41.4274   $41.43   $41.45   $41.40  
  Purchase #6 $222.61   8.329%   $241.1512   $241.15   $241.15   $241.20  
  Purchase #7 $160.30   10.314%   $176.8333   $176.83   $176.85   $176.80  
  7 purchase totals = $1,021.23       $1,123.9718   $1,123.96   $1,123.95   $1,124.00