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 $35.58   8.306%   $38.5353   $38.54   $38.55   $38.50  
  Purchase #2 $222.36   13.870%   $253.2013   $253.20   $253.20   $253.20  
  Purchase #3 $219.68   3.257%   $226.835   $226.84   $226.85   $226.80  
  Purchase #4 $103.96   5.339%   $109.5104   $109.51   $109.50   $109.50  
  Purchase #5 $42.40   6.416%   $45.1204   $45.12   $45.10   $45.10  
  Purchase #6 $221.35   12.506%   $249.032   $249.03   $249.05   $249.00  
  Purchase #7 $80.87   8.631%   $87.8499   $87.85   $87.85   $87.80  
  7 purchase totals = $926.20       $1,010.0843   $1,010.09   $1,010.10   $1,009.90