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 $62.77   10.468%   $69.3408   $69.34   $69.35   $69.30  
  Purchase #2 $241.29   6.770%   $257.6253   $257.63   $257.65   $257.60  
  Purchase #3 $15.82   11.156%   $17.5849   $17.58   $17.60   $17.60  
  Purchase #4 $79.96   11.843%   $89.4297   $89.43   $89.45   $89.40  
  Purchase #5 $46.33   6.679%   $49.4244   $49.42   $49.40   $49.40  
  Purchase #6 $62.93   11.242%   $70.0046   $70.00   $70.00   $70.00  
  Purchase #7 $183.82   13.407%   $208.4647   $208.46   $208.45   $208.50  
  7 purchase totals = $692.92       $761.8744   $761.86   $761.90   $761.80