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 $176.39   5.866%   $186.737   $186.74   $186.75   $186.70  
  Purchase #2 $34.96   11.675%   $39.0416   $39.04   $39.05   $39.00  
  Purchase #3 $166.61   10.603%   $184.2757   $184.28   $184.30   $184.30  
  Purchase #4 $114.84   3.441%   $118.7916   $118.79   $118.80   $118.80  
  Purchase #5 $53.64   7.252%   $57.53   $57.53   $57.55   $57.50  
  Purchase #6 $181.80   3.852%   $188.8029   $188.80   $188.80   $188.80  
  Purchase #7 $82.63   3.425%   $85.4601   $85.46   $85.45   $85.50  
  7 purchase totals = $810.87       $860.6389   $860.64   $860.70   $860.60