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 $55.99   13.334%   $63.4557   $63.46   $63.45   $63.50  
  Purchase #2 $176.51   4.817%   $185.0125   $185.01   $185.00   $185.00  
  Purchase #3 $104.92   13.631%   $119.2216   $119.22   $119.20   $119.20  
  Purchase #4 $214.37   7.273%   $229.9611   $229.96   $229.95   $230.00  
  Purchase #5 $88.73   9.392%   $97.0635   $97.06   $97.05   $97.10  
  Purchase #6 $103.26   7.668%   $111.178   $111.18   $111.20   $111.20  
  Purchase #7 $171.59   5.255%   $180.6071   $180.61   $180.60   $180.60  
  7 purchase totals = $915.37       $986.4995   $986.50   $986.45   $986.60