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 $161.74   3.216%   $166.9416   $166.94   $166.95   $166.90  
  Purchase #2 $70.91   6.186%   $75.2965   $75.30   $75.30   $75.30  
  Purchase #3 $129.84   13.368%   $147.197   $147.20   $147.20   $147.20  
  Purchase #4 $86.73   13.233%   $98.207   $98.21   $98.20   $98.20  
  Purchase #5 $209.55   7.605%   $225.4863   $225.49   $225.50   $225.50  
  Purchase #6 $25.34   6.866%   $27.0798   $27.08   $27.10   $27.10  
  Purchase #7 $118.45   3.577%   $122.687   $122.69   $122.70   $122.70  
  7 purchase totals = $802.56       $862.8952   $862.91   $862.95   $862.90