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 $24.50   3.359%   $25.323   $25.32   $25.30   $25.30  
  Purchase #2 $241.28   5.538%   $254.6421   $254.64   $254.65   $254.60  
  Purchase #3 $170.75   12.546%   $192.1723   $192.17   $192.15   $192.20  
  Purchase #4 $24.58   12.782%   $27.7218   $27.72   $27.70   $27.70  
  Purchase #5 $13.56   4.831%   $14.2151   $14.22   $14.20   $14.20  
  Purchase #6 $226.93   6.320%   $241.272   $241.27   $241.25   $241.30  
  Purchase #7 $208.75   13.830%   $237.6201   $237.62   $237.60   $237.60  
  7 purchase totals = $910.35       $992.9664   $992.96   $992.85   $992.90