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 $106.83   12.533%   $120.219   $120.22   $120.20   $120.20  
  Purchase #2 $197.75   3.470%   $204.6119   $204.61   $204.60   $204.60  
  Purchase #3 $70.90   4.702%   $74.2337   $74.23   $74.25   $74.20  
  Purchase #4 $54.59   6.352%   $58.0576   $58.06   $58.05   $58.10  
  Purchase #5 $217.87   7.303%   $233.781   $233.78   $233.80   $233.80  
  Purchase #6 $100.69   13.387%   $114.1694   $114.17   $114.15   $114.20  
  Purchase #7 $208.81   11.288%   $232.3805   $232.38   $232.40   $232.40  
  7 purchase totals = $957.44       $1,037.4531   $1,037.45   $1,037.45   $1,037.50