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 $95.30   3.409%   $98.5488   $98.55   $98.55   $98.50  
  Purchase #2 $68.74   3.535%   $71.17   $71.17   $71.15   $71.20  
  Purchase #3 $56.47   12.679%   $63.6298   $63.63   $63.65   $63.60  
  Purchase #4 $190.99   12.133%   $214.1628   $214.16   $214.15   $214.20  
  Purchase #5 $56.56   12.694%   $63.7397   $63.74   $63.75   $63.70  
  Purchase #6 $16.75   8.419%   $18.1602   $18.16   $18.15   $18.20  
  Purchase #7 $61.63   13.760%   $70.1103   $70.11   $70.10   $70.10  
  7 purchase totals = $546.44       $599.5216   $599.52   $599.50   $599.50