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 $57.51   5.521%   $60.6851   $60.69   $60.70   $60.70  
  Purchase #2 $85.38   12.295%   $95.8775   $95.88   $95.90   $95.90  
  Purchase #3 $122.68   5.526%   $129.4593   $129.46   $129.45   $129.50  
  Purchase #4 $196.62   5.392%   $207.2218   $207.22   $207.20   $207.20  
  Purchase #5 $155.83   11.712%   $174.0808   $174.08   $174.10   $174.10  
  Purchase #6 $115.44   11.848%   $129.1173   $129.12   $129.10   $129.10  
  Purchase #7 $227.99   9.502%   $249.6536   $249.65   $249.65   $249.70  
  7 purchase totals = $961.45       $1,046.0954   $1,046.10   $1,046.10   $1,046.20