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 $65.41   5.857%   $69.2411   $69.24   $69.25   $69.20  
  Purchase #2 $125.40   7.499%   $134.8037   $134.80   $134.80   $134.80  
  Purchase #3 $250.35   4.788%   $262.3368   $262.34   $262.35   $262.30  
  Purchase #4 $133.61   11.689%   $149.2277   $149.23   $149.25   $149.20  
  Purchase #5 $134.77   6.508%   $143.5408   $143.54   $143.55   $143.50  
  Purchase #6 $248.60   5.784%   $262.979   $262.98   $263.00   $263.00  
  Purchase #7 $173.60   6.352%   $184.6271   $184.63   $184.65   $184.60  
  7 purchase totals = $1,131.74       $1,206.7562   $1,206.76   $1,206.85   $1,206.60