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 $10.37   11.460%   $11.5584   $11.56   $11.55   $11.60  
  Purchase #2 $24.74   10.221%   $27.2687   $27.27   $27.25   $27.30  
  Purchase #3 $64.78   8.181%   $70.0797   $70.08   $70.10   $70.10  
  Purchase #4 $90.93   3.509%   $94.1207   $94.12   $94.10   $94.10  
  Purchase #5 $245.73   5.431%   $259.0756   $259.08   $259.10   $259.10  
  Purchase #6 $242.88   9.827%   $266.7478   $266.75   $266.75   $266.70  
  Purchase #7 $114.80   7.513%   $123.4249   $123.42   $123.40   $123.40  
  7 purchase totals = $794.23       $852.2758   $852.28   $852.25   $852.30