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 $229.86   7.328%   $246.7041   $246.70   $246.70   $246.70  
  Purchase #2 $79.74   7.817%   $85.9733   $85.97   $85.95   $86.00  
  Purchase #3 $114.38   5.209%   $120.3381   $120.34   $120.35   $120.30  
  Purchase #4 $213.39   5.377%   $224.864   $224.86   $224.85   $224.90  
  Purchase #5 $65.64   10.554%   $72.5676   $72.57   $72.55   $72.60  
  Purchase #6 $73.35   3.597%   $75.9884   $75.99   $76.00   $76.00  
  Purchase #7 $154.63   13.508%   $175.5174   $175.52   $175.50   $175.50  
  7 purchase totals = $930.99       $1,001.9529   $1,001.95   $1,001.90   $1,002.00