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 $162.59   8.608%   $176.5857   $176.59   $176.60   $176.60  
  Purchase #2 $168.38   9.286%   $184.0158   $184.02   $184.00   $184.00  
  Purchase #3 $70.35   11.414%   $78.3797   $78.38   $78.40   $78.40  
  Purchase #4 $158.36   6.116%   $168.0453   $168.05   $168.05   $168.00  
  Purchase #5 $112.92   10.587%   $124.8748   $124.87   $124.85   $124.90  
  Purchase #6 $225.66   11.425%   $251.4417   $251.44   $251.45   $251.40  
  Purchase #7 $224.33   10.267%   $247.362   $247.36   $247.35   $247.40  
  7 purchase totals = $1,122.59       $1,230.7050   $1,230.71   $1,230.70   $1,230.70