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 $166.99   10.523%   $184.5624   $184.56   $184.55   $184.60  
  Purchase #2 $94.81   4.196%   $98.7882   $98.79   $98.80   $98.80  
  Purchase #3 $104.95   9.353%   $114.766   $114.77   $114.75   $114.80  
  Purchase #4 $168.59   7.440%   $181.1331   $181.13   $181.15   $181.10  
  Purchase #5 $16.61   13.657%   $18.8784   $18.88   $18.90   $18.90  
  Purchase #6 $90.80   5.692%   $95.9683   $95.97   $95.95   $96.00  
  Purchase #7 $100.37   13.562%   $113.9822   $113.98   $114.00   $114.00  
  7 purchase totals = $743.12       $808.0786   $808.08   $808.10   $808.20