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 $144.60   10.126%   $159.2422   $159.24   $159.25   $159.20  
  Purchase #2 $43.51   3.175%   $44.8914   $44.89   $44.90   $44.90  
  Purchase #3 $156.77   4.848%   $164.3702   $164.37   $164.35   $164.40  
  Purchase #4 $183.49   7.335%   $196.949   $196.95   $196.95   $196.90  
  Purchase #5 $214.80   4.676%   $224.844   $224.84   $224.85   $224.80  
  Purchase #6 $200.26   13.539%   $227.3732   $227.37   $227.35   $227.40  
  Purchase #7 $174.86   7.504%   $187.9815   $187.98   $188.00   $188.00  
  7 purchase totals = $1,118.29       $1,205.6515   $1,205.64   $1,205.65   $1,205.60