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 $54.49   12.662%   $61.3895   $61.39   $61.40   $61.40  
  Purchase #2 $125.32   13.238%   $141.9099   $141.91   $141.90   $141.90  
  Purchase #3 $91.61   3.822%   $95.1113   $95.11   $95.10   $95.10  
  Purchase #4 $242.86   5.164%   $255.4013   $255.40   $255.40   $255.40  
  Purchase #5 $121.58   5.487%   $128.2511   $128.25   $128.25   $128.30  
  Purchase #6 $234.66   13.364%   $266.02   $266.02   $266.00   $266.00  
  Purchase #7 $16.79   13.231%   $19.0115   $19.01   $19.00   $19.00  
  7 purchase totals = $887.31       $967.0946   $967.09   $967.05   $967.10