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 $206.66   12.272%   $232.0213   $232.02   $232.00   $232.00  
  Purchase #2 $177.86   8.370%   $192.7469   $192.75   $192.75   $192.70  
  Purchase #3 $250.67   12.658%   $282.3998   $282.40   $282.40   $282.40  
  Purchase #4 $143.32   12.768%   $161.6191   $161.62   $161.60   $161.60  
  Purchase #5 $39.58   3.558%   $40.9883   $40.99   $41.00   $41.00  
  Purchase #6 $140.96   6.271%   $149.7996   $149.80   $149.80   $149.80  
  Purchase #7 $208.60   6.291%   $221.723   $221.72   $221.70   $221.70  
  7 purchase totals = $1,167.65       $1,281.2980   $1,281.30   $1,281.25   $1,281.20