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 $5.47   7.762%   $5.8946   $5.89   $5.90   $5.90  
  Purchase #2 $239.57   11.125%   $266.2222   $266.22   $266.20   $266.20  
  Purchase #3 $159.70   10.301%   $176.1507   $176.15   $176.15   $176.20  
  Purchase #4 $45.98   10.390%   $50.7573   $50.76   $50.75   $50.80  
  Purchase #5 $170.73   8.442%   $185.143   $185.14   $185.15   $185.10  
  Purchase #6 $237.73   4.512%   $248.4564   $248.46   $248.45   $248.50  
  Purchase #7 $79.80   8.754%   $86.7857   $86.79   $86.80   $86.80  
  7 purchase totals = $938.98       $1,019.4099   $1,019.41   $1,019.40   $1,019.50