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 $53.62   11.665%   $59.8748   $59.87   $59.85   $59.90  
  Purchase #2 $115.93   13.295%   $131.3429   $131.34   $131.35   $131.30  
  Purchase #3 $176.25   4.701%   $184.5355   $184.54   $184.55   $184.50  
  Purchase #4 $89.37   8.647%   $97.0978   $97.10   $97.10   $97.10  
  Purchase #5 $203.85   5.234%   $214.5195   $214.52   $214.50   $214.50  
  Purchase #6 $164.32   13.392%   $186.3257   $186.33   $186.35   $186.30  
  Purchase #7 $23.65   6.690%   $25.2322   $25.23   $25.25   $25.20  
  7 purchase totals = $826.99       $898.9284   $898.93   $898.95   $898.80