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 $213.80   5.202%   $224.9219   $224.92   $224.90   $224.90  
  Purchase #2 $136.65   12.287%   $153.4402   $153.44   $153.45   $153.40  
  Purchase #3 $73.89   13.671%   $83.9915   $83.99   $84.00   $84.00  
  Purchase #4 $85.66   12.822%   $96.6433   $96.64   $96.65   $96.60  
  Purchase #5 $86.60   10.793%   $95.9467   $95.95   $95.95   $95.90  
  Purchase #6 $15.75   9.237%   $17.2048   $17.20   $17.20   $17.20  
  Purchase #7 $86.92   9.238%   $94.9497   $94.95   $94.95   $94.90  
  7 purchase totals = $699.27       $767.0981   $767.09   $767.10   $766.90