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 $126.34   11.581%   $140.9714   $140.97   $140.95   $141.00  
  Purchase #2 $86.26   8.642%   $93.7146   $93.71   $93.70   $93.70  
  Purchase #3 $79.34   5.648%   $83.8211   $83.82   $83.80   $83.80  
  Purchase #4 $191.91   7.773%   $206.8272   $206.83   $206.85   $206.80  
  Purchase #5 $237.40   6.560%   $252.9734   $252.97   $252.95   $253.00  
  Purchase #6 $97.32   3.775%   $100.9938   $100.99   $101.00   $101.00  
  Purchase #7 $138.65   6.543%   $147.7219   $147.72   $147.70   $147.70  
  7 purchase totals = $957.22       $1,027.0234   $1,027.01   $1,026.95   $1,027.00