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 $232.65   8.868%   $253.2814   $253.28   $253.30   $253.30  
  Purchase #2 $184.45   5.832%   $195.2071   $195.21   $195.20   $195.20  
  Purchase #3 $76.99   8.635%   $83.6381   $83.64   $83.65   $83.60  
  Purchase #4 $213.59   10.773%   $236.6001   $236.60   $236.60   $236.60  
  Purchase #5 $9.44   9.654%   $10.3513   $10.35   $10.35   $10.40  
  Purchase #6 $79.34   4.132%   $82.6183   $82.62   $82.60   $82.60  
  Purchase #7 $64.92   4.572%   $67.8881   $67.89   $67.90   $67.90  
  7 purchase totals = $861.38       $929.5844   $929.59   $929.60   $929.60