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 $113.93   7.668%   $122.6662   $122.67   $122.65   $122.70  
  Purchase #2 $176.61   13.164%   $199.8589   $199.86   $199.85   $199.90  
  Purchase #3 $23.37   12.252%   $26.2333   $26.23   $26.25   $26.20  
  Purchase #4 $209.53   7.861%   $226.0012   $226.00   $226.00   $226.00  
  Purchase #5 $99.67   5.799%   $105.4499   $105.45   $105.45   $105.40  
  Purchase #6 $45.98   8.381%   $49.8336   $49.83   $49.85   $49.80  
  Purchase #7 $44.73   3.844%   $46.4494   $46.45   $46.45   $46.40  
  7 purchase totals = $713.82       $776.4925   $776.49   $776.50   $776.40