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 $69.84   5.616%   $73.7622   $73.76   $73.75   $73.80  
  Purchase #2 $113.30   10.380%   $125.0605   $125.06   $125.05   $125.10  
  Purchase #3 $186.71   3.802%   $193.8087   $193.81   $193.80   $193.80  
  Purchase #4 $134.43   5.819%   $142.2525   $142.25   $142.25   $142.30  
  Purchase #5 $149.75   5.456%   $157.9204   $157.92   $157.90   $157.90  
  Purchase #6 $180.26   9.329%   $197.0765   $197.08   $197.10   $197.10  
  Purchase #7 $237.55   3.722%   $246.3916   $246.39   $246.40   $246.40  
  7 purchase totals = $1,071.84       $1,136.2724   $1,136.27   $1,136.25   $1,136.40