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 $165.65   8.383%   $179.5364   $179.54   $179.55   $179.50  
  Purchase #2 $250.88   4.131%   $261.2439   $261.24   $261.25   $261.20  
  Purchase #3 $67.62   10.275%   $74.568   $74.57   $74.55   $74.60  
  Purchase #4 $113.90   11.667%   $127.1887   $127.19   $127.20   $127.20  
  Purchase #5 $175.58   10.409%   $193.8561   $193.86   $193.85   $193.90  
  Purchase #6 $22.41   8.749%   $24.3707   $24.37   $24.35   $24.40  
  Purchase #7 $172.64   8.449%   $187.2264   $187.23   $187.25   $187.20  
  7 purchase totals = $968.68       $1,047.9902   $1,048.00   $1,048.00   $1,048.00