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 $58.54   3.795%   $60.7616   $60.76   $60.75   $60.80  
  Purchase #2 $250.66   12.183%   $281.1979   $281.20   $281.20   $281.20  
  Purchase #3 $44.35   7.253%   $47.5667   $47.57   $47.55   $47.60  
  Purchase #4 $202.54   9.724%   $222.235   $222.24   $222.25   $222.20  
  Purchase #5 $67.36   8.501%   $73.0863   $73.09   $73.10   $73.10  
  Purchase #6 $11.65   11.638%   $13.0058   $13.01   $13.00   $13.00  
  Purchase #7 $147.63   13.362%   $167.3563   $167.36   $167.35   $167.40  
  7 purchase totals = $782.73       $865.2096   $865.23   $865.20   $865.30