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 $59.86   8.760%   $65.1037   $65.10   $65.10   $65.10  
  Purchase #2 $166.64   9.524%   $182.5108   $182.51   $182.50   $182.50  
  Purchase #3 $43.54   8.453%   $47.2204   $47.22   $47.20   $47.20  
  Purchase #4 $122.88   13.670%   $139.6777   $139.68   $139.70   $139.70  
  Purchase #5 $77.71   5.537%   $82.0128   $82.01   $82.00   $82.00  
  Purchase #6 $62.96   7.609%   $67.7506   $67.75   $67.75   $67.80  
  Purchase #7 $208.28   4.586%   $217.8317   $217.83   $217.85   $217.80  
  7 purchase totals = $741.87       $802.1077   $802.10   $802.10   $802.10