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 $206.83   8.433%   $224.272   $224.27   $224.25   $224.30  
  Purchase #2 $94.92   13.111%   $107.365   $107.37   $107.35   $107.40  
  Purchase #3 $154.79   5.108%   $162.6967   $162.70   $162.70   $162.70  
  Purchase #4 $36.64   5.521%   $38.6629   $38.66   $38.65   $38.70  
  Purchase #5 $128.51   3.175%   $132.5902   $132.59   $132.60   $132.60  
  Purchase #6 $197.45   4.849%   $207.0244   $207.02   $207.00   $207.00  
  Purchase #7 $79.50   6.138%   $84.3797   $84.38   $84.40   $84.40  
  7 purchase totals = $898.64       $956.9909   $956.99   $956.95   $957.10