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 $209.46   13.730%   $238.2189   $238.22   $238.20   $238.20  
  Purchase #2 $13.47   12.829%   $15.1981   $15.20   $15.20   $15.20  
  Purchase #3 $68.99   10.108%   $75.9635   $75.96   $75.95   $76.00  
  Purchase #4 $233.57   6.376%   $248.4624   $248.46   $248.45   $248.50  
  Purchase #5 $191.75   13.367%   $217.3812   $217.38   $217.40   $217.40  
  Purchase #6 $176.79   4.759%   $185.2034   $185.20   $185.20   $185.20  
  Purchase #7 $98.81   4.710%   $103.464   $103.46   $103.45   $103.50  
  7 purchase totals = $992.84       $1,083.8915   $1,083.88   $1,083.85   $1,084.00