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 $210.59   13.801%   $239.6535   $239.65   $239.65   $239.70  
  Purchase #2 $8.39   6.325%   $8.9207   $8.92   $8.90   $8.90  
  Purchase #3 $82.59   5.270%   $86.9425   $86.94   $86.95   $86.90  
  Purchase #4 $156.61   8.472%   $169.878   $169.88   $169.90   $169.90  
  Purchase #5 $124.29   9.450%   $136.0354   $136.04   $136.05   $136.00  
  Purchase #6 $185.27   6.177%   $196.7141   $196.71   $196.70   $196.70  
  Purchase #7 $46.43   8.726%   $50.4815   $50.48   $50.50   $50.50  
  7 purchase totals = $814.17       $888.6257   $888.62   $888.65   $888.60