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 $86.43   11.854%   $96.6754   $96.68   $96.70   $96.70  
  Purchase #2 $6.58   13.454%   $7.4653   $7.47   $7.45   $7.50  
  Purchase #3 $157.97   13.146%   $178.7367   $178.74   $178.75   $178.70  
  Purchase #4 $27.94   7.702%   $30.0919   $30.09   $30.10   $30.10  
  Purchase #5 $239.73   5.543%   $253.0182   $253.02   $253.00   $253.00  
  Purchase #6 $119.57   11.739%   $133.6063   $133.61   $133.60   $133.60  
  Purchase #7 $204.81   13.292%   $232.0333   $232.03   $232.05   $232.00  
  7 purchase totals = $843.03       $931.6271   $931.64   $931.65   $931.60