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 $73.91   5.272%   $77.8065   $77.81   $77.80   $77.80  
  Purchase #2 $210.61   11.741%   $235.3377   $235.34   $235.35   $235.30  
  Purchase #3 $176.95   6.239%   $187.9899   $187.99   $188.00   $188.00  
  Purchase #4 $223.53   7.335%   $239.9259   $239.93   $239.95   $239.90  
  Purchase #5 $81.68   7.226%   $87.5822   $87.58   $87.60   $87.60  
  Purchase #6 $174.75   3.715%   $181.242   $181.24   $181.25   $181.20  
  Purchase #7 $34.56   4.331%   $36.0568   $36.06   $36.05   $36.10  
  7 purchase totals = $975.99       $1,045.9410   $1,045.95   $1,046.00   $1,045.90