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 $164.47   5.472%   $173.4698   $173.47   $173.45   $173.50  
  Purchase #2 $183.69   13.555%   $208.5892   $208.59   $208.60   $208.60  
  Purchase #3 $236.26   13.579%   $268.3417   $268.34   $268.35   $268.30  
  Purchase #4 $210.65   5.395%   $222.0146   $222.01   $222.00   $222.00  
  Purchase #5 $44.45   10.402%   $49.0737   $49.07   $49.05   $49.10  
  Purchase #6 $21.77   4.256%   $22.6965   $22.70   $22.70   $22.70  
  Purchase #7 $5.67   13.700%   $6.4468   $6.45   $6.45   $6.40  
  7 purchase totals = $866.96       $950.6323   $950.63   $950.60   $950.60