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 $221.43   12.745%   $249.6513   $249.65   $249.65   $249.70  
  Purchase #2 $144.33   5.774%   $152.6636   $152.66   $152.65   $152.70  
  Purchase #3 $219.90   3.226%   $226.994   $226.99   $227.00   $227.00  
  Purchase #4 $97.67   6.856%   $104.3663   $104.37   $104.35   $104.40  
  Purchase #5 $185.46   11.373%   $206.5524   $206.55   $206.55   $206.60  
  Purchase #6 $47.47   7.221%   $50.8978   $50.90   $50.90   $50.90  
  Purchase #7 $217.37   4.557%   $227.2756   $227.28   $227.30   $227.30  
  7 purchase totals = $1,133.63       $1,218.4010   $1,218.40   $1,218.40   $1,218.60