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 $68.63   11.521%   $76.5369   $76.54   $76.55   $76.50  
  Purchase #2 $208.87   9.805%   $229.3497   $229.35   $229.35   $229.30  
  Purchase #3 $48.51   3.860%   $50.3825   $50.38   $50.40   $50.40  
  Purchase #4 $192.83   8.633%   $209.477   $209.48   $209.50   $209.50  
  Purchase #5 $234.30   8.267%   $253.6696   $253.67   $253.65   $253.70  
  Purchase #6 $26.89   4.839%   $28.1912   $28.19   $28.20   $28.20  
  Purchase #7 $91.58   4.445%   $95.6507   $95.65   $95.65   $95.70  
  7 purchase totals = $871.61       $943.2576   $943.26   $943.30   $943.30