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 $100.69   3.508%   $104.2222   $104.22   $104.20   $104.20  
  Purchase #2 $213.58   13.773%   $242.9964   $243.00   $243.00   $243.00  
  Purchase #3 $164.25   6.187%   $174.4121   $174.41   $174.40   $174.40  
  Purchase #4 $5.27   3.829%   $5.4718   $5.47   $5.45   $5.50  
  Purchase #5 $14.75   8.122%   $15.948   $15.95   $15.95   $15.90  
  Purchase #6 $166.52   6.510%   $177.3605   $177.36   $177.35   $177.40  
  Purchase #7 $63.41   4.217%   $66.084   $66.08   $66.10   $66.10  
  7 purchase totals = $728.47       $786.4950   $786.49   $786.45   $786.50