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 $166.75   5.669%   $176.2031   $176.20   $176.20   $176.20  
  Purchase #2 $244.27   6.217%   $259.4563   $259.46   $259.45   $259.50  
  Purchase #3 $233.64   6.586%   $249.0275   $249.03   $249.05   $249.00  
  Purchase #4 $139.40   11.726%   $155.746   $155.75   $155.75   $155.70  
  Purchase #5 $160.27   13.726%   $182.2687   $182.27   $182.25   $182.30  
  Purchase #6 $153.63   11.719%   $171.6339   $171.63   $171.65   $171.60  
  Purchase #7 $154.27   11.818%   $172.5016   $172.50   $172.50   $172.50  
  7 purchase totals = $1,252.23       $1,366.8371   $1,366.84   $1,366.85   $1,366.80