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 $47.71   12.551%   $53.6981   $53.70   $53.70   $53.70  
  Purchase #2 $159.67   8.683%   $173.5341   $173.53   $173.55   $173.50  
  Purchase #3 $100.60   10.585%   $111.2485   $111.25   $111.25   $111.20  
  Purchase #4 $49.78   8.405%   $53.964   $53.96   $53.95   $54.00  
  Purchase #5 $7.81   3.317%   $8.0691   $8.07   $8.05   $8.10  
  Purchase #6 $248.73   11.698%   $277.8264   $277.83   $277.85   $277.80  
  Purchase #7 $248.74   5.453%   $262.3038   $262.30   $262.30   $262.30  
  7 purchase totals = $863.04       $940.6440   $940.64   $940.65   $940.60