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 $68.67   11.348%   $76.4627   $76.46   $76.45   $76.50  
  Purchase #2 $185.84   12.379%   $208.8451   $208.85   $208.85   $208.80  
  Purchase #3 $126.44   3.579%   $130.9653   $130.97   $130.95   $131.00  
  Purchase #4 $154.71   8.439%   $167.766   $167.77   $167.75   $167.80  
  Purchase #5 $187.83   9.575%   $205.8147   $205.81   $205.80   $205.80  
  Purchase #6 $161.52   4.500%   $168.7884   $168.79   $168.80   $168.80  
  Purchase #7 $39.90   11.778%   $44.5994   $44.60   $44.60   $44.60  
  7 purchase totals = $924.91       $1,003.2416   $1,003.25   $1,003.20   $1,003.30