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 $76.88   12.153%   $86.2232   $86.22   $86.20   $86.20  
  Purchase #2 $180.66   9.234%   $197.3421   $197.34   $197.35   $197.30  
  Purchase #3 $205.55   3.800%   $213.3609   $213.36   $213.35   $213.40  
  Purchase #4 $142.59   5.604%   $150.5807   $150.58   $150.60   $150.60  
  Purchase #5 $135.25   10.660%   $149.6677   $149.67   $149.65   $149.70  
  Purchase #6 $154.47   3.316%   $159.5922   $159.59   $159.60   $159.60  
  Purchase #7 $52.89   13.856%   $60.2184   $60.22   $60.20   $60.20  
  7 purchase totals = $948.29       $1,016.9852   $1,016.98   $1,016.95   $1,017.00