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 $226.30   11.482%   $252.2838   $252.28   $252.30   $252.30  
  Purchase #2 $246.77   4.130%   $256.9616   $256.96   $256.95   $257.00  
  Purchase #3 $119.90   12.140%   $134.4559   $134.46   $134.45   $134.50  
  Purchase #4 $166.43   10.109%   $183.2544   $183.25   $183.25   $183.30  
  Purchase #5 $207.64   5.855%   $219.7973   $219.80   $219.80   $219.80  
  Purchase #6 $25.34   3.228%   $26.158   $26.16   $26.15   $26.20  
  Purchase #7 $144.38   6.537%   $153.8181   $153.82   $153.80   $153.80  
  7 purchase totals = $1,136.76       $1,226.7291   $1,226.73   $1,226.70   $1,226.90