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 $61.41   11.726%   $68.6109   $68.61   $68.60   $68.60  
  Purchase #2 $23.28   13.710%   $26.4717   $26.47   $26.45   $26.50  
  Purchase #3 $79.43   4.862%   $83.2919   $83.29   $83.30   $83.30  
  Purchase #4 $53.98   7.814%   $58.198   $58.20   $58.20   $58.20  
  Purchase #5 $94.34   4.537%   $98.6202   $98.62   $98.60   $98.60  
  Purchase #6 $208.74   11.117%   $231.9456   $231.95   $231.95   $231.90  
  Purchase #7 $12.61   3.699%   $13.0764   $13.08   $13.10   $13.10  
  7 purchase totals = $533.79       $580.2147   $580.22   $580.20   $580.20