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 $59.37   7.617%   $63.8922   $63.89   $63.90   $63.90  
  Purchase #2 $189.92   12.265%   $213.2137   $213.21   $213.20   $213.20  
  Purchase #3 $34.76   10.147%   $38.2871   $38.29   $38.30   $38.30  
  Purchase #4 $247.43   7.451%   $265.866   $265.87   $265.85   $265.90  
  Purchase #5 $201.29   9.403%   $220.2173   $220.22   $220.20   $220.20  
  Purchase #6 $83.37   12.552%   $93.8346   $93.83   $93.85   $93.80  
  Purchase #7 $107.89   10.717%   $119.4526   $119.45   $119.45   $119.50  
  7 purchase totals = $924.03       $1,014.7635   $1,014.76   $1,014.75   $1,014.80