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 $141.76   10.456%   $156.5824   $156.58   $156.60   $156.60  
  Purchase #2 $114.49   11.145%   $127.2499   $127.25   $127.25   $127.20  
  Purchase #3 $201.44   8.284%   $218.1273   $218.13   $218.15   $218.10  
  Purchase #4 $176.48   12.636%   $198.78   $198.78   $198.80   $198.80  
  Purchase #5 $59.41   4.486%   $62.0751   $62.08   $62.10   $62.10  
  Purchase #6 $131.28   5.290%   $138.2247   $138.22   $138.20   $138.20  
  Purchase #7 $46.32   12.364%   $52.047   $52.05   $52.05   $52.00  
  7 purchase totals = $871.18       $953.0864   $953.09   $953.15   $953.00