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 $60.68   5.533%   $64.0374   $64.04   $64.05   $64.00  
  Purchase #2 $237.86   7.837%   $256.5011   $256.50   $256.50   $256.50  
  Purchase #3 $72.91   3.699%   $75.6069   $75.61   $75.60   $75.60  
  Purchase #4 $245.96   5.372%   $259.173   $259.17   $259.15   $259.20  
  Purchase #5 $115.85   3.586%   $120.0044   $120.00   $120.00   $120.00  
  Purchase #6 $235.32   5.640%   $248.592   $248.59   $248.60   $248.60  
  Purchase #7 $107.51   9.746%   $117.9879   $117.99   $118.00   $118.00  
  7 purchase totals = $1,076.09       $1,141.9027   $1,141.90   $1,141.90   $1,141.90