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 $225.66   11.238%   $251.0197   $251.02   $251.00   $251.00  
  Purchase #2 $146.36   4.242%   $152.5686   $152.57   $152.55   $152.60  
  Purchase #3 $67.60   11.335%   $75.2625   $75.26   $75.25   $75.30  
  Purchase #4 $86.94   4.278%   $90.6593   $90.66   $90.65   $90.70  
  Purchase #5 $196.29   8.308%   $212.5978   $212.60   $212.60   $212.60  
  Purchase #6 $166.81   5.147%   $175.3957   $175.40   $175.40   $175.40  
  Purchase #7 $51.98   12.800%   $58.6334   $58.63   $58.65   $58.60  
  7 purchase totals = $941.64       $1,016.1370   $1,016.14   $1,016.10   $1,016.20