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 $51.76   13.170%   $58.5768   $58.58   $58.60   $58.60  
  Purchase #2 $115.46   13.239%   $130.7457   $130.75   $130.75   $130.70  
  Purchase #3 $217.26   10.646%   $240.3895   $240.39   $240.40   $240.40  
  Purchase #4 $97.25   9.813%   $106.7931   $106.79   $106.80   $106.80  
  Purchase #5 $148.48   5.735%   $156.9953   $157.00   $157.00   $157.00  
  Purchase #6 $176.29   9.211%   $192.5281   $192.53   $192.55   $192.50  
  Purchase #7 $186.51   6.732%   $199.0659   $199.07   $199.05   $199.10  
  7 purchase totals = $993.01       $1,085.0944   $1,085.11   $1,085.15   $1,085.10