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 $77.29   12.509%   $86.9582   $86.96   $86.95   $87.00  
  Purchase #2 $145.33   8.856%   $158.2004   $158.20   $158.20   $158.20  
  Purchase #3 $126.82   13.365%   $143.7695   $143.77   $143.75   $143.80  
  Purchase #4 $197.89   4.844%   $207.4758   $207.48   $207.50   $207.50  
  Purchase #5 $103.87   13.453%   $117.8436   $117.84   $117.85   $117.80  
  Purchase #6 $237.90   6.112%   $252.4404   $252.44   $252.45   $252.40  
  Purchase #7 $26.96   4.630%   $28.2082   $28.21   $28.20   $28.20  
  7 purchase totals = $916.06       $994.8961   $994.90   $994.90   $994.90