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 $64.41   6.638%   $68.6855   $68.69   $68.70   $68.70  
  Purchase #2 $198.94   4.755%   $208.3996   $208.40   $208.40   $208.40  
  Purchase #3 $104.54   10.391%   $115.4028   $115.40   $115.40   $115.40  
  Purchase #4 $200.93   6.518%   $214.0266   $214.03   $214.05   $214.00  
  Purchase #5 $55.88   4.254%   $58.2571   $58.26   $58.25   $58.30  
  Purchase #6 $41.69   11.719%   $46.5757   $46.58   $46.60   $46.60  
  Purchase #7 $90.86   3.833%   $94.3427   $94.34   $94.35   $94.30  
  7 purchase totals = $757.25       $805.6900   $805.70   $805.75   $805.70