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 $243.97   8.532%   $264.7855   $264.79   $264.80   $264.80  
  Purchase #2 $213.41   11.430%   $237.8028   $237.80   $237.80   $237.80  
  Purchase #3 $226.89   9.586%   $248.6397   $248.64   $248.65   $248.60  
  Purchase #4 $25.58   3.578%   $26.4953   $26.50   $26.50   $26.50  
  Purchase #5 $162.77   3.379%   $168.27   $168.27   $168.25   $168.30  
  Purchase #6 $171.51   6.342%   $182.3872   $182.39   $182.40   $182.40  
  Purchase #7 $186.51   10.468%   $206.0339   $206.03   $206.05   $206.00  
  7 purchase totals = $1,230.64       $1,334.4144   $1,334.42   $1,334.45   $1,334.40