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 $164.37   7.298%   $176.3657   $176.37   $176.35   $176.40  
  Purchase #2 $44.66   10.718%   $49.4467   $49.45   $49.45   $49.40  
  Purchase #3 $66.29   6.795%   $70.7944   $70.79   $70.80   $70.80  
  Purchase #4 $85.76   11.722%   $95.8128   $95.81   $95.80   $95.80  
  Purchase #5 $245.94   8.324%   $266.412   $266.41   $266.40   $266.40  
  Purchase #6 $178.37   8.128%   $192.8679   $192.87   $192.85   $192.90  
  Purchase #7 $178.79   3.297%   $184.6847   $184.68   $184.70   $184.70  
  7 purchase totals = $964.18       $1,036.3842   $1,036.38   $1,036.35   $1,036.40