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 $24.44   4.659%   $25.5787   $25.58   $25.60   $25.60  
  Purchase #2 $213.71   11.168%   $237.5771   $237.58   $237.60   $237.60  
  Purchase #3 $226.72   7.834%   $244.4812   $244.48   $244.50   $244.50  
  Purchase #4 $176.54   12.826%   $199.183   $199.18   $199.20   $199.20  
  Purchase #5 $16.90   10.491%   $18.673   $18.67   $18.65   $18.70  
  Purchase #6 $77.28   4.331%   $80.627   $80.63   $80.65   $80.60  
  Purchase #7 $62.51   9.730%   $68.5922   $68.59   $68.60   $68.60  
  7 purchase totals = $798.10       $874.7122   $874.71   $874.80   $874.80