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 $248.33   5.772%   $262.6636   $262.66   $262.65   $262.70  
  Purchase #2 $223.32   3.542%   $231.23   $231.23   $231.25   $231.20  
  Purchase #3 $37.65   5.460%   $39.7057   $39.71   $39.70   $39.70  
  Purchase #4 $141.32   13.409%   $160.2696   $160.27   $160.25   $160.30  
  Purchase #5 $97.79   7.500%   $105.1243   $105.12   $105.10   $105.10  
  Purchase #6 $61.26   12.829%   $69.119   $69.12   $69.10   $69.10  
  Purchase #7 $109.68   8.733%   $119.2584   $119.26   $119.25   $119.30  
  7 purchase totals = $919.35       $987.3706   $987.37   $987.30   $987.40