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 $27.65   6.110%   $29.3394   $29.34   $29.35   $29.30  
  Purchase #2 $239.46   7.844%   $258.2432   $258.24   $258.25   $258.20  
  Purchase #3 $24.88   4.491%   $25.9974   $26.00   $26.00   $26.00  
  Purchase #4 $18.45   13.104%   $20.8677   $20.87   $20.85   $20.90  
  Purchase #5 $242.75   11.254%   $270.0691   $270.07   $270.05   $270.10  
  Purchase #6 $236.80   5.311%   $249.3764   $249.38   $249.40   $249.40  
  Purchase #7 $87.95   13.759%   $100.051   $100.05   $100.05   $100.10  
  7 purchase totals = $877.94       $953.9442   $953.95   $953.95   $954.00