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 $168.59   9.853%   $185.2012   $185.20   $185.20   $185.20  
  Purchase #2 $55.72   11.303%   $62.018   $62.02   $62.00   $62.00  
  Purchase #3 $242.57   12.467%   $272.8112   $272.81   $272.80   $272.80  
  Purchase #4 $65.36   13.724%   $74.33   $74.33   $74.35   $74.30  
  Purchase #5 $236.76   9.217%   $258.5822   $258.58   $258.60   $258.60  
  Purchase #6 $224.26   12.534%   $252.3687   $252.37   $252.35   $252.40  
  Purchase #7 $182.54   10.469%   $201.6501   $201.65   $201.65   $201.70  
  7 purchase totals = $1,175.80       $1,306.9614   $1,306.96   $1,306.95   $1,307.00