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 $130.30   9.343%   $142.4739   $142.47   $142.45   $142.50  
  Purchase #2 $140.63   3.852%   $146.0471   $146.05   $146.05   $146.00  
  Purchase #3 $177.84   10.676%   $196.8262   $196.83   $196.85   $196.80  
  Purchase #4 $47.94   6.316%   $50.9679   $50.97   $50.95   $51.00  
  Purchase #5 $92.95   3.377%   $96.0889   $96.09   $96.10   $96.10  
  Purchase #6 $173.74   3.112%   $179.1468   $179.15   $179.15   $179.10  
  Purchase #7 $26.59   8.613%   $28.8802   $28.88   $28.90   $28.90  
  7 purchase totals = $789.99       $840.4310   $840.44   $840.45   $840.40