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 $182.84   7.552%   $196.6481   $196.65   $196.65   $196.60  
  Purchase #2 $92.78   13.633%   $105.4287   $105.43   $105.45   $105.40  
  Purchase #3 $171.93   6.474%   $183.0607   $183.06   $183.05   $183.10  
  Purchase #4 $205.41   10.465%   $226.9062   $226.91   $226.90   $226.90  
  Purchase #5 $146.59   7.506%   $157.593   $157.59   $157.60   $157.60  
  Purchase #6 $239.90   5.310%   $252.6387   $252.64   $252.65   $252.60  
  Purchase #7 $171.64   9.504%   $187.9527   $187.95   $187.95   $188.00  
  7 purchase totals = $1,211.09       $1,310.2281   $1,310.23   $1,310.25   $1,310.20