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 $65.53   10.501%   $72.4113   $72.41   $72.40   $72.40  
  Purchase #2 $108.54   5.463%   $114.4695   $114.47   $114.45   $114.50  
  Purchase #3 $87.93   9.832%   $96.5753   $96.58   $96.60   $96.60  
  Purchase #4 $115.61   10.614%   $127.8808   $127.88   $127.90   $127.90  
  Purchase #5 $202.35   11.814%   $226.2556   $226.26   $226.25   $226.30  
  Purchase #6 $103.70   6.124%   $110.0506   $110.05   $110.05   $110.10  
  Purchase #7 $41.75   10.576%   $46.1655   $46.17   $46.15   $46.20  
  7 purchase totals = $725.41       $793.8086   $793.82   $793.80   $794.00