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 $65.38   4.793%   $68.5137   $68.51   $68.50   $68.50  
  Purchase #2 $11.78   7.583%   $12.6733   $12.67   $12.65   $12.70  
  Purchase #3 $114.68   7.453%   $123.2271   $123.23   $123.25   $123.20  
  Purchase #4 $62.51   9.273%   $68.3066   $68.31   $68.30   $68.30  
  Purchase #5 $193.69   8.581%   $210.3105   $210.31   $210.30   $210.30  
  Purchase #6 $200.93   8.269%   $217.5449   $217.54   $217.55   $217.50  
  Purchase #7 $229.86   8.406%   $249.182   $249.18   $249.20   $249.20  
  7 purchase totals = $878.83       $949.7581   $949.75   $949.75   $949.70