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 $93.47   10.278%   $103.0768   $103.08   $103.10   $103.10  
  Purchase #2 $139.65   5.867%   $147.8433   $147.84   $147.85   $147.80  
  Purchase #3 $117.57   8.232%   $127.2484   $127.25   $127.25   $127.20  
  Purchase #4 $197.63   7.175%   $211.81   $211.81   $211.80   $211.80  
  Purchase #5 $43.71   11.176%   $48.595   $48.60   $48.60   $48.60  
  Purchase #6 $17.49   10.771%   $19.3738   $19.37   $19.35   $19.40  
  Purchase #7 $87.46   5.357%   $92.1452   $92.15   $92.15   $92.10  
  7 purchase totals = $696.98       $750.0925   $750.10   $750.10   $750.00