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 $54.64   12.670%   $61.5629   $61.56   $61.55   $61.60  
  Purchase #2 $87.28   5.185%   $91.8055   $91.81   $91.80   $91.80  
  Purchase #3 $174.57   11.306%   $194.3069   $194.31   $194.30   $194.30  
  Purchase #4 $76.77   12.242%   $86.1682   $86.17   $86.15   $86.20  
  Purchase #5 $233.94   8.490%   $253.8015   $253.80   $253.80   $253.80  
  Purchase #6 $80.40   12.540%   $90.4822   $90.48   $90.50   $90.50  
  Purchase #7 $208.87   3.513%   $216.2076   $216.21   $216.20   $216.20  
  7 purchase totals = $916.47       $994.3348   $994.34   $994.30   $994.40