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 $84.70   12.417%   $95.2172   $95.22   $95.20   $95.20  
  Purchase #2 $50.94   9.710%   $55.8863   $55.89   $55.90   $55.90  
  Purchase #3 $6.26   8.377%   $6.7844   $6.78   $6.80   $6.80  
  Purchase #4 $176.79   13.267%   $200.2447   $200.24   $200.25   $200.20  
  Purchase #5 $222.67   6.587%   $237.3373   $237.34   $237.35   $237.30  
  Purchase #6 $73.48   5.608%   $77.6008   $77.60   $77.60   $77.60  
  Purchase #7 $182.95   5.406%   $192.8403   $192.84   $192.85   $192.80  
  7 purchase totals = $797.79       $865.9110   $865.91   $865.95   $865.80