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 $151.68   8.759%   $164.9657   $164.97   $164.95   $165.00  
  Purchase #2 $99.26   12.474%   $111.6417   $111.64   $111.65   $111.60  
  Purchase #3 $135.80   6.244%   $144.2794   $144.28   $144.30   $144.30  
  Purchase #4 $86.44   11.292%   $96.2008   $96.20   $96.20   $96.20  
  Purchase #5 $232.34   7.201%   $249.0708   $249.07   $249.05   $249.10  
  Purchase #6 $26.49   12.759%   $29.8699   $29.87   $29.85   $29.90  
  Purchase #7 $88.80   10.556%   $98.1737   $98.17   $98.15   $98.20  
  7 purchase totals = $820.81       $894.2020   $894.20   $894.15   $894.30