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 $95.41   8.532%   $103.5504   $103.55   $103.55   $103.60  
  Purchase #2 $249.37   9.758%   $273.7035   $273.70   $273.70   $273.70  
  Purchase #3 $154.42   13.349%   $175.0335   $175.03   $175.05   $175.00  
  Purchase #4 $250.61   4.603%   $262.1456   $262.15   $262.15   $262.10  
  Purchase #5 $185.92   9.463%   $203.5136   $203.51   $203.50   $203.50  
  Purchase #6 $141.44   11.786%   $158.1101   $158.11   $158.10   $158.10  
  Purchase #7 $194.33   11.712%   $217.0899   $217.09   $217.10   $217.10  
  7 purchase totals = $1,271.50       $1,393.1466   $1,393.14   $1,393.15   $1,393.10