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 $220.93   11.358%   $246.0232   $246.02   $246.00   $246.00  
  Purchase #2 $213.93   5.673%   $226.0662   $226.07   $226.05   $226.10  
  Purchase #3 $67.37   8.102%   $72.8283   $72.83   $72.85   $72.80  
  Purchase #4 $44.25   11.335%   $49.2657   $49.27   $49.25   $49.30  
  Purchase #5 $61.57   3.478%   $63.7114   $63.71   $63.70   $63.70  
  Purchase #6 $157.89   8.265%   $170.9396   $170.94   $170.95   $170.90  
  Purchase #7 $174.31   4.604%   $182.3352   $182.34   $182.35   $182.30  
  7 purchase totals = $940.25       $1,011.1696   $1,011.18   $1,011.15   $1,011.10