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 $61.96   6.547%   $66.0165   $66.02   $66.00   $66.00  
  Purchase #2 $201.56   12.599%   $226.9545   $226.95   $226.95   $227.00  
  Purchase #3 $44.55   10.246%   $49.1146   $49.11   $49.10   $49.10  
  Purchase #4 $234.45   11.434%   $261.257   $261.26   $261.25   $261.30  
  Purchase #5 $172.80   11.332%   $192.3817   $192.38   $192.40   $192.40  
  Purchase #6 $7.56   8.804%   $8.2256   $8.23   $8.25   $8.20  
  Purchase #7 $111.75   6.870%   $119.4272   $119.43   $119.45   $119.40  
  7 purchase totals = $834.63       $923.3771   $923.38   $923.40   $923.40