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 $228.44   3.631%   $236.7347   $236.73   $236.75   $236.70  
  Purchase #2 $161.58   10.739%   $178.9321   $178.93   $178.95   $178.90  
  Purchase #3 $115.32   10.517%   $127.4482   $127.45   $127.45   $127.40  
  Purchase #4 $157.61   3.585%   $163.2603   $163.26   $163.25   $163.30  
  Purchase #5 $225.80   11.333%   $251.3899   $251.39   $251.40   $251.40  
  Purchase #6 $135.87   3.642%   $140.8184   $140.82   $140.80   $140.80  
  Purchase #7 $238.80   12.806%   $269.3807   $269.38   $269.40   $269.40  
  7 purchase totals = $1,263.42       $1,367.9643   $1,367.96   $1,368.00   $1,367.90