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 $186.83   12.812%   $210.7667   $210.77   $210.75   $210.80  
  Purchase #2 $247.69   11.847%   $277.0338   $277.03   $277.05   $277.00  
  Purchase #3 $113.89   3.669%   $118.0686   $118.07   $118.05   $118.10  
  Purchase #4 $160.86   10.491%   $177.7358   $177.74   $177.75   $177.70  
  Purchase #5 $74.67   6.282%   $79.3608   $79.36   $79.35   $79.40  
  Purchase #6 $198.97   5.821%   $210.552   $210.55   $210.55   $210.60  
  Purchase #7 $249.76   6.867%   $266.911   $266.91   $266.90   $266.90  
  7 purchase totals = $1,232.67       $1,340.4287   $1,340.43   $1,340.40   $1,340.50