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 $56.80   13.865%   $64.6753   $64.68   $64.70   $64.70  
  Purchase #2 $112.39   6.369%   $119.5481   $119.55   $119.55   $119.50  
  Purchase #3 $72.93   5.807%   $77.165   $77.17   $77.15   $77.20  
  Purchase #4 $149.70   9.468%   $163.8736   $163.87   $163.85   $163.90  
  Purchase #5 $243.65   8.724%   $264.906   $264.91   $264.90   $264.90  
  Purchase #6 $243.99   9.366%   $266.8421   $266.84   $266.85   $266.80  
  Purchase #7 $23.72   6.549%   $25.2734   $25.27   $25.25   $25.30  
  7 purchase totals = $903.18       $982.2835   $982.29   $982.25   $982.30