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 $113.71   7.852%   $122.6385   $122.64   $122.65   $122.60  
  Purchase #2 $165.68   12.399%   $186.2227   $186.22   $186.20   $186.20  
  Purchase #3 $11.54   13.157%   $13.0583   $13.06   $13.05   $13.10  
  Purchase #4 $59.55   6.138%   $63.2052   $63.21   $63.20   $63.20  
  Purchase #5 $192.91   4.258%   $201.1241   $201.12   $201.10   $201.10  
  Purchase #6 $111.26   8.395%   $120.6003   $120.60   $120.60   $120.60  
  Purchase #7 $141.86   10.221%   $156.3595   $156.36   $156.35   $156.40  
  7 purchase totals = $796.51       $863.2086   $863.21   $863.15   $863.20