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 $235.36   5.449%   $248.1848   $248.18   $248.20   $248.20  
  Purchase #2 $249.97   13.746%   $284.3309   $284.33   $284.35   $284.30  
  Purchase #3 $9.75   6.244%   $10.3588   $10.36   $10.35   $10.40  
  Purchase #4 $188.61   9.166%   $205.898   $205.90   $205.90   $205.90  
  Purchase #5 $12.48   10.253%   $13.7596   $13.76   $13.75   $13.80  
  Purchase #6 $186.67   11.684%   $208.4805   $208.48   $208.50   $208.50  
  Purchase #7 $73.52   10.808%   $81.466   $81.47   $81.45   $81.50  
  7 purchase totals = $956.36       $1,052.4786   $1,052.48   $1,052.50   $1,052.60