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 $87.33   5.596%   $92.217   $92.22   $92.20   $92.20  
  Purchase #2 $132.89   3.448%   $137.472   $137.47   $137.45   $137.50  
  Purchase #3 $23.78   11.826%   $26.5922   $26.59   $26.60   $26.60  
  Purchase #4 $144.30   8.484%   $156.5424   $156.54   $156.55   $156.50  
  Purchase #5 $5.53   6.564%   $5.893   $5.89   $5.90   $5.90  
  Purchase #6 $75.62   13.309%   $85.6843   $85.68   $85.70   $85.70  
  Purchase #7 $119.97   8.171%   $129.7727   $129.77   $129.75   $129.80  
  7 purchase totals = $589.42       $634.1736   $634.16   $634.15   $634.20