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 $59.93   10.530%   $66.2406   $66.24   $66.25   $66.20  
  Purchase #2 $49.52   8.130%   $53.546   $53.55   $53.55   $53.50  
  Purchase #3 $233.93   7.772%   $252.111   $252.11   $252.10   $252.10  
  Purchase #4 $211.30   12.519%   $237.7526   $237.75   $237.75   $237.80  
  Purchase #5 $90.97   8.118%   $98.3549   $98.35   $98.35   $98.40  
  Purchase #6 $200.68   5.173%   $211.0612   $211.06   $211.05   $211.10  
  Purchase #7 $130.71   7.105%   $139.9969   $140.00   $140.00   $140.00  
  7 purchase totals = $977.04       $1,059.0632   $1,059.06   $1,059.05   $1,059.10