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 $180.86   13.204%   $204.7408   $204.74   $204.75   $204.70  
  Purchase #2 $115.40   11.230%   $128.3594   $128.36   $128.35   $128.40  
  Purchase #3 $136.59   11.540%   $152.3525   $152.35   $152.35   $152.40  
  Purchase #4 $219.59   7.215%   $235.4334   $235.43   $235.45   $235.40  
  Purchase #5 $242.81   9.714%   $266.3966   $266.40   $266.40   $266.40  
  Purchase #6 $219.75   13.722%   $249.9041   $249.90   $249.90   $249.90  
  Purchase #7 $160.82   8.239%   $174.07   $174.07   $174.05   $174.10  
  7 purchase totals = $1,275.82       $1,411.2568   $1,411.25   $1,411.25   $1,411.30