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 $239.71   5.290%   $252.3907   $252.39   $252.40   $252.40  
  Purchase #2 $49.46   11.234%   $55.0163   $55.02   $55.00   $55.00  
  Purchase #3 $64.31   4.161%   $66.9859   $66.99   $67.00   $67.00  
  Purchase #4 $213.42   10.805%   $236.48   $236.48   $236.50   $236.50  
  Purchase #5 $83.50   11.214%   $92.8637   $92.86   $92.85   $92.90  
  Purchase #6 $169.68   13.531%   $192.6394   $192.64   $192.65   $192.60  
  Purchase #7 $173.92   12.771%   $196.1313   $196.13   $196.15   $196.10  
  7 purchase totals = $994.00       $1,092.5073   $1,092.51   $1,092.55   $1,092.50