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 $61.73   11.770%   $68.9956   $69.00   $69.00   $69.00  
  Purchase #2 $123.70   7.786%   $133.3313   $133.33   $133.35   $133.30  
  Purchase #3 $196.30   10.549%   $217.0077   $217.01   $217.00   $217.00  
  Purchase #4 $50.64   9.772%   $55.5885   $55.59   $55.60   $55.60  
  Purchase #5 $117.96   13.333%   $133.6876   $133.69   $133.70   $133.70  
  Purchase #6 $215.79   6.655%   $230.1508   $230.15   $230.15   $230.20  
  Purchase #7 $83.63   3.801%   $86.8088   $86.81   $86.80   $86.80  
  7 purchase totals = $849.75       $925.5703   $925.58   $925.60   $925.60