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 $61.34   4.123%   $63.869   $63.87   $63.85   $63.90  
  Purchase #2 $16.81   5.291%   $17.6994   $17.70   $17.70   $17.70  
  Purchase #3 $200.83   5.626%   $212.1287   $212.13   $212.15   $212.10  
  Purchase #4 $170.42   13.311%   $193.1046   $193.10   $193.10   $193.10  
  Purchase #5 $64.48   10.832%   $71.4645   $71.46   $71.45   $71.50  
  Purchase #6 $206.67   6.391%   $219.8783   $219.88   $219.90   $219.90  
  Purchase #7 $162.69   13.478%   $184.6174   $184.62   $184.60   $184.60  
  7 purchase totals = $883.24       $962.7619   $962.76   $962.75   $962.80