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 $243.34   10.782%   $269.5769   $269.58   $269.60   $269.60  
  Purchase #2 $119.69   9.127%   $130.6141   $130.61   $130.60   $130.60  
  Purchase #3 $190.53   6.194%   $202.3314   $202.33   $202.35   $202.30  
  Purchase #4 $82.97   4.758%   $86.9177   $86.92   $86.90   $86.90  
  Purchase #5 $225.64   7.814%   $243.2715   $243.27   $243.25   $243.30  
  Purchase #6 $79.60   7.113%   $85.2619   $85.26   $85.25   $85.30  
  Purchase #7 $91.33   11.488%   $101.822   $101.82   $101.80   $101.80  
  7 purchase totals = $1,033.10       $1,119.7955   $1,119.79   $1,119.75   $1,119.80