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 $64.61   3.446%   $66.8365   $66.84   $66.85   $66.80  
  Purchase #2 $196.57   10.563%   $217.3337   $217.33   $217.35   $217.30  
  Purchase #3 $161.91   11.305%   $180.2139   $180.21   $180.20   $180.20  
  Purchase #4 $62.45   8.328%   $67.6508   $67.65   $67.65   $67.70  
  Purchase #5 $194.44   13.831%   $221.333   $221.33   $221.35   $221.30  
  Purchase #6 $158.67   13.550%   $180.1698   $180.17   $180.15   $180.20  
  Purchase #7 $248.44   13.779%   $282.6725   $282.67   $282.65   $282.70  
  7 purchase totals = $1,087.09       $1,216.2102   $1,216.20   $1,216.20   $1,216.20