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 $184.88   11.801%   $206.6977   $206.70   $206.70   $206.70  
  Purchase #2 $23.47   3.529%   $24.2983   $24.30   $24.30   $24.30  
  Purchase #3 $85.36   4.545%   $89.2396   $89.24   $89.25   $89.20  
  Purchase #4 $21.27   3.557%   $22.0266   $22.03   $22.05   $22.00  
  Purchase #5 $214.60   11.452%   $239.176   $239.18   $239.20   $239.20  
  Purchase #6 $226.44   9.140%   $247.1366   $247.14   $247.15   $247.10  
  Purchase #7 $190.67   9.104%   $208.0286   $208.03   $208.05   $208.00  
  7 purchase totals = $946.69       $1,036.6034   $1,036.62   $1,036.70   $1,036.50