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 $65.97   11.149%   $73.325   $73.33   $73.35   $73.30  
  Purchase #2 $177.75   8.266%   $192.4428   $192.44   $192.45   $192.40  
  Purchase #3 $115.67   7.483%   $124.3256   $124.33   $124.35   $124.30  
  Purchase #4 $129.52   5.602%   $136.7757   $136.78   $136.80   $136.80  
  Purchase #5 $159.76   9.185%   $174.434   $174.43   $174.45   $174.40  
  Purchase #6 $7.90   11.708%   $8.8249   $8.82   $8.80   $8.80  
  Purchase #7 $153.41   13.318%   $173.8411   $173.84   $173.85   $173.80  
  7 purchase totals = $809.98       $883.9691   $883.97   $884.05   $883.80