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 $58.51   8.738%   $63.6226   $63.62   $63.60   $63.60  
  Purchase #2 $85.83   10.372%   $94.7323   $94.73   $94.75   $94.70  
  Purchase #3 $203.88   7.126%   $218.4085   $218.41   $218.40   $218.40  
  Purchase #4 $68.51   7.171%   $73.4229   $73.42   $73.40   $73.40  
  Purchase #5 $224.82   12.204%   $252.257   $252.26   $252.25   $252.30  
  Purchase #6 $160.61   5.213%   $168.9826   $168.98   $169.00   $169.00  
  Purchase #7 $48.37   8.316%   $52.3924   $52.39   $52.40   $52.40  
  7 purchase totals = $850.53       $923.8183   $923.81   $923.80   $923.80