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 $142.44   8.771%   $154.9334   $154.93   $154.95   $154.90  
  Purchase #2 $206.55   6.172%   $219.2983   $219.30   $219.30   $219.30  
  Purchase #3 $155.96   4.645%   $163.2043   $163.20   $163.20   $163.20  
  Purchase #4 $214.65   8.688%   $233.2988   $233.30   $233.30   $233.30  
  Purchase #5 $143.77   7.369%   $154.3644   $154.36   $154.35   $154.40  
  Purchase #6 $233.41   3.436%   $241.43   $241.43   $241.45   $241.40  
  Purchase #7 $182.93   3.157%   $188.7051   $188.71   $188.70   $188.70  
  7 purchase totals = $1,279.71       $1,355.2343   $1,355.23   $1,355.25   $1,355.20