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 $59.84   13.230%   $67.7568   $67.76   $67.75   $67.80  
  Purchase #2 $83.67   4.755%   $87.6485   $87.65   $87.65   $87.60  
  Purchase #3 $209.36   5.572%   $221.0255   $221.03   $221.05   $221.00  
  Purchase #4 $33.69   9.473%   $36.8815   $36.88   $36.90   $36.90  
  Purchase #5 $139.84   3.250%   $144.3848   $144.38   $144.40   $144.40  
  Purchase #6 $226.32   10.475%   $250.027   $250.03   $250.05   $250.00  
  Purchase #7 $186.99   11.495%   $208.4845   $208.48   $208.50   $208.50  
  7 purchase totals = $939.71       $1,016.2086   $1,016.21   $1,016.30   $1,016.20