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 $197.82   8.582%   $214.7969   $214.80   $214.80   $214.80  
  Purchase #2 $224.97   10.151%   $247.8067   $247.81   $247.80   $247.80  
  Purchase #3 $42.66   11.350%   $47.5019   $47.50   $47.50   $47.50  
  Purchase #4 $206.65   12.425%   $232.3263   $232.33   $232.35   $232.30  
  Purchase #5 $76.54   12.611%   $86.1925   $86.19   $86.20   $86.20  
  Purchase #6 $11.53   13.169%   $13.0484   $13.05   $13.05   $13.00  
  Purchase #7 $82.66   3.484%   $85.5399   $85.54   $85.55   $85.50  
  7 purchase totals = $842.83       $927.2126   $927.22   $927.25   $927.10