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 $197.99   8.568%   $214.9538   $214.95   $214.95   $215.00  
  Purchase #2 $108.66   13.680%   $123.5247   $123.52   $123.50   $123.50  
  Purchase #3 $250.75   7.622%   $269.8622   $269.86   $269.85   $269.90  
  Purchase #4 $67.33   3.803%   $69.8906   $69.89   $69.90   $69.90  
  Purchase #5 $35.58   4.359%   $37.1309   $37.13   $37.15   $37.10  
  Purchase #6 $70.38   5.493%   $74.246   $74.25   $74.25   $74.20  
  Purchase #7 $196.50   6.473%   $209.2194   $209.22   $209.20   $209.20  
  7 purchase totals = $927.19       $998.8276   $998.82   $998.80   $998.80