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 $34.72   5.416%   $36.6004   $36.60   $36.60   $36.60  
  Purchase #2 $84.76   9.187%   $92.5469   $92.55   $92.55   $92.50  
  Purchase #3 $28.55   10.591%   $31.5737   $31.57   $31.55   $31.60  
  Purchase #4 $223.80   5.660%   $236.4671   $236.47   $236.45   $236.50  
  Purchase #5 $66.93   10.785%   $74.1484   $74.15   $74.15   $74.10  
  Purchase #6 $144.58   9.606%   $158.4684   $158.47   $158.45   $158.50  
  Purchase #7 $85.90   9.652%   $94.1911   $94.19   $94.20   $94.20  
  7 purchase totals = $669.24       $723.9960   $724.00   $723.95   $724.00