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 $211.47   8.587%   $229.6289   $229.63   $229.65   $229.60  
  Purchase #2 $14.85   5.621%   $15.6847   $15.68   $15.70   $15.70  
  Purchase #3 $148.91   7.777%   $160.4907   $160.49   $160.50   $160.50  
  Purchase #4 $126.90   8.487%   $137.67   $137.67   $137.65   $137.70  
  Purchase #5 $126.58   12.627%   $142.5633   $142.56   $142.55   $142.60  
  Purchase #6 $153.50   8.348%   $166.3142   $166.31   $166.30   $166.30  
  Purchase #7 $13.81   4.866%   $14.482   $14.48   $14.50   $14.50  
  7 purchase totals = $796.02       $866.8338   $866.82   $866.85   $866.90