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 $68.25   11.146%   $75.8571   $75.86   $75.85   $75.90  
  Purchase #2 $114.87   10.408%   $126.8257   $126.83   $126.85   $126.80  
  Purchase #3 $18.71   4.265%   $19.508   $19.51   $19.50   $19.50  
  Purchase #4 $111.53   4.626%   $116.6894   $116.69   $116.70   $116.70  
  Purchase #5 $176.94   3.668%   $183.4302   $183.43   $183.45   $183.40  
  Purchase #6 $15.43   10.142%   $16.9949   $16.99   $17.00   $17.00  
  Purchase #7 $81.96   3.440%   $84.7794   $84.78   $84.80   $84.80  
  7 purchase totals = $587.69       $624.0847   $624.09   $624.15   $624.10