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 $40.97   12.313%   $46.0146   $46.01   $46.00   $46.00  
  Purchase #2 $109.63   7.317%   $117.6516   $117.65   $117.65   $117.70  
  Purchase #3 $34.66   5.718%   $36.6419   $36.64   $36.65   $36.60  
  Purchase #4 $147.95   10.599%   $163.6312   $163.63   $163.65   $163.60  
  Purchase #5 $68.66   11.425%   $76.5044   $76.50   $76.50   $76.50  
  Purchase #6 $196.58   8.854%   $213.9852   $213.99   $214.00   $214.00  
  Purchase #7 $212.91   6.660%   $227.0898   $227.09   $227.10   $227.10  
  7 purchase totals = $811.36       $881.5187   $881.51   $881.55   $881.50