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 $57.32   10.329%   $63.2406   $63.24   $63.25   $63.20  
  Purchase #2 $208.27   13.479%   $236.3427   $236.34   $236.35   $236.30  
  Purchase #3 $70.55   6.397%   $75.0631   $75.06   $75.05   $75.10  
  Purchase #4 $248.63   6.629%   $265.1117   $265.11   $265.10   $265.10  
  Purchase #5 $94.97   13.212%   $107.5174   $107.52   $107.50   $107.50  
  Purchase #6 $166.60   5.434%   $175.653   $175.65   $175.65   $175.70  
  Purchase #7 $35.98   5.491%   $37.9557   $37.96   $37.95   $38.00  
  7 purchase totals = $882.32       $960.8842   $960.88   $960.85   $960.90