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 $52.92   10.110%   $58.2702   $58.27   $58.25   $58.30  
  Purchase #2 $30.64   6.738%   $32.7045   $32.70   $32.70   $32.70  
  Purchase #3 $223.80   13.274%   $253.5072   $253.51   $253.50   $253.50  
  Purchase #4 $207.47   9.134%   $226.4203   $226.42   $226.40   $226.40  
  Purchase #5 $79.57   9.359%   $87.017   $87.02   $87.00   $87.00  
  Purchase #6 $228.83   10.501%   $252.8594   $252.86   $252.85   $252.90  
  Purchase #7 $94.40   4.298%   $98.4573   $98.46   $98.45   $98.50  
  7 purchase totals = $917.63       $1,009.2359   $1,009.24   $1,009.15   $1,009.30