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 $58.76   6.241%   $62.4272   $62.43   $62.45   $62.40  
  Purchase #2 $38.58   8.206%   $41.7459   $41.75   $41.75   $41.70  
  Purchase #3 $135.26   7.814%   $145.8292   $145.83   $145.85   $145.80  
  Purchase #4 $210.49   6.729%   $224.6539   $224.65   $224.65   $224.70  
  Purchase #5 $187.90   5.109%   $197.4998   $197.50   $197.50   $197.50  
  Purchase #6 $193.78   6.626%   $206.6199   $206.62   $206.60   $206.60  
  Purchase #7 $30.94   11.505%   $34.4996   $34.50   $34.50   $34.50  
  7 purchase totals = $855.71       $913.2755   $913.28   $913.30   $913.20