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 $37.78   10.200%   $41.6336   $41.63   $41.65   $41.60  
  Purchase #2 $167.71   8.542%   $182.0358   $182.04   $182.05   $182.00  
  Purchase #3 $70.43   3.554%   $72.9331   $72.93   $72.95   $72.90  
  Purchase #4 $80.58   6.316%   $85.6694   $85.67   $85.65   $85.70  
  Purchase #5 $152.36   8.464%   $165.2558   $165.26   $165.25   $165.30  
  Purchase #6 $207.83   3.115%   $214.3039   $214.30   $214.30   $214.30  
  Purchase #7 $71.64   4.543%   $74.8946   $74.89   $74.90   $74.90  
  7 purchase totals = $788.33       $836.7262   $836.72   $836.75   $836.70