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 $56.74   12.705%   $63.9488   $63.95   $63.95   $63.90  
  Purchase #2 $135.27   4.690%   $141.6142   $141.61   $141.60   $141.60  
  Purchase #3 $146.42   7.562%   $157.4923   $157.49   $157.50   $157.50  
  Purchase #4 $36.83   12.329%   $41.3708   $41.37   $41.35   $41.40  
  Purchase #5 $187.58   6.166%   $199.1462   $199.15   $199.15   $199.10  
  Purchase #6 $58.54   8.712%   $63.64   $63.64   $63.65   $63.60  
  Purchase #7 $140.64   9.631%   $154.185   $154.19   $154.20   $154.20  
  7 purchase totals = $762.02       $821.3973   $821.40   $821.40   $821.30