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 $84.38   13.397%   $95.6844   $95.68   $95.70   $95.70  
  Purchase #2 $144.47   13.606%   $164.1266   $164.13   $164.15   $164.10  
  Purchase #3 $94.45   12.782%   $106.5226   $106.52   $106.50   $106.50  
  Purchase #4 $210.99   7.186%   $226.1517   $226.15   $226.15   $226.20  
  Purchase #5 $42.61   11.189%   $47.3776   $47.38   $47.40   $47.40  
  Purchase #6 $145.53   12.774%   $164.12   $164.12   $164.10   $164.10  
  Purchase #7 $115.61   6.465%   $123.0842   $123.08   $123.10   $123.10  
  7 purchase totals = $838.04       $927.0671   $927.06   $927.10   $927.10