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 $143.41   5.524%   $151.332   $151.33   $151.35   $151.30  
  Purchase #2 $96.36   10.724%   $106.6936   $106.69   $106.70   $106.70  
  Purchase #3 $53.46   9.298%   $58.4307   $58.43   $58.45   $58.40  
  Purchase #4 $238.72   8.342%   $258.634   $258.63   $258.65   $258.60  
  Purchase #5 $103.60   10.361%   $114.334   $114.33   $114.35   $114.30  
  Purchase #6 $40.88   6.521%   $43.5458   $43.55   $43.55   $43.50  
  Purchase #7 $246.91   6.510%   $262.9838   $262.98   $263.00   $263.00  
  7 purchase totals = $923.34       $995.9539   $995.94   $996.05   $995.80