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 $61.96   10.737%   $68.6126   $68.61   $68.60   $68.60  
  Purchase #2 $189.27   11.854%   $211.7061   $211.71   $211.70   $211.70  
  Purchase #3 $164.46   10.847%   $182.299   $182.30   $182.30   $182.30  
  Purchase #4 $234.48   4.817%   $245.7749   $245.77   $245.75   $245.80  
  Purchase #5 $235.34   9.473%   $257.6338   $257.63   $257.65   $257.60  
  Purchase #6 $149.95   7.572%   $161.3042   $161.30   $161.30   $161.30  
  Purchase #7 $137.25   11.577%   $153.1394   $153.14   $153.15   $153.10  
  7 purchase totals = $1,172.71       $1,280.4700   $1,280.46   $1,280.45   $1,280.40