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 $229.50   6.760%   $245.0142   $245.01   $245.00   $245.00  
  Purchase #2 $70.27   6.397%   $74.7652   $74.77   $74.75   $74.80  
  Purchase #3 $239.49   5.855%   $253.5121   $253.51   $253.50   $253.50  
  Purchase #4 $187.51   6.621%   $199.925   $199.93   $199.95   $199.90  
  Purchase #5 $52.47   10.599%   $58.0313   $58.03   $58.05   $58.00  
  Purchase #6 $21.32   6.695%   $22.7474   $22.75   $22.75   $22.70  
  Purchase #7 $66.70   5.498%   $70.3672   $70.37   $70.35   $70.40  
  7 purchase totals = $867.26       $924.3624   $924.37   $924.35   $924.30