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 $236.98   10.801%   $262.5762   $262.58   $262.60   $262.60  
  Purchase #2 $130.96   12.234%   $146.9816   $146.98   $147.00   $147.00  
  Purchase #3 $30.65   12.314%   $34.4242   $34.42   $34.40   $34.40  
  Purchase #4 $234.32   10.837%   $259.7133   $259.71   $259.70   $259.70  
  Purchase #5 $35.25   7.531%   $37.9047   $37.90   $37.90   $37.90  
  Purchase #6 $250.42   10.315%   $276.2508   $276.25   $276.25   $276.30  
  Purchase #7 $25.64   4.241%   $26.7274   $26.73   $26.75   $26.70  
  7 purchase totals = $944.22       $1,044.5782   $1,044.57   $1,044.60   $1,044.60