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 $24.29   8.254%   $26.2949   $26.29   $26.30   $26.30  
  Purchase #2 $166.87   4.866%   $174.9899   $174.99   $175.00   $175.00  
  Purchase #3 $149.52   12.791%   $168.6451   $168.65   $168.65   $168.60  
  Purchase #4 $177.70   4.657%   $185.9755   $185.98   $186.00   $186.00  
  Purchase #5 $67.30   11.437%   $74.9971   $75.00   $75.00   $75.00  
  Purchase #6 $147.81   6.754%   $157.7931   $157.79   $157.80   $157.80  
  Purchase #7 $164.61   7.674%   $177.2422   $177.24   $177.25   $177.20  
  7 purchase totals = $898.10       $965.9378   $965.94   $966.00   $965.90