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 $88.85   7.476%   $95.4924   $95.49   $95.50   $95.50  
  Purchase #2 $115.53   5.231%   $121.5734   $121.57   $121.55   $121.60  
  Purchase #3 $231.90   4.320%   $241.9181   $241.92   $241.90   $241.90  
  Purchase #4 $21.78   6.185%   $23.1271   $23.13   $23.15   $23.10  
  Purchase #5 $138.36   13.815%   $157.4744   $157.47   $157.45   $157.50  
  Purchase #6 $239.66   7.733%   $258.1929   $258.19   $258.20   $258.20  
  Purchase #7 $50.96   7.670%   $54.8686   $54.87   $54.85   $54.90  
  7 purchase totals = $887.04       $952.6469   $952.64   $952.60   $952.70