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 $209.26   12.492%   $235.4008   $235.40   $235.40   $235.40  
  Purchase #2 $72.95   3.553%   $75.5419   $75.54   $75.55   $75.50  
  Purchase #3 $159.90   11.714%   $178.6307   $178.63   $178.65   $178.60  
  Purchase #4 $51.48   11.384%   $57.3405   $57.34   $57.35   $57.30  
  Purchase #5 $132.68   10.445%   $146.5384   $146.54   $146.55   $146.50  
  Purchase #6 $203.66   10.714%   $225.4801   $225.48   $225.50   $225.50  
  Purchase #7 $219.81   13.142%   $248.6974   $248.70   $248.70   $248.70  
  7 purchase totals = $1,049.74       $1,167.6298   $1,167.63   $1,167.70   $1,167.50