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 $217.33   11.720%   $242.8011   $242.80   $242.80   $242.80  
  Purchase #2 $17.84   6.234%   $18.9521   $18.95   $18.95   $19.00  
  Purchase #3 $106.89   4.491%   $111.6904   $111.69   $111.70   $111.70  
  Purchase #4 $152.33   3.681%   $157.9373   $157.94   $157.95   $157.90  
  Purchase #5 $211.83   3.186%   $218.5789   $218.58   $218.60   $218.60  
  Purchase #6 $232.90   5.611%   $245.968   $245.97   $245.95   $246.00  
  Purchase #7 $34.29   10.185%   $37.7824   $37.78   $37.80   $37.80  
  7 purchase totals = $973.41       $1,033.7102   $1,033.71   $1,033.75   $1,033.80