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 $156.65   6.650%   $167.0672   $167.07   $167.05   $167.10  
  Purchase #2 $69.44   6.524%   $73.9703   $73.97   $73.95   $74.00  
  Purchase #3 $56.62   11.732%   $63.2627   $63.26   $63.25   $63.30  
  Purchase #4 $22.31   10.105%   $24.5644   $24.56   $24.55   $24.60  
  Purchase #5 $90.65   3.819%   $94.1119   $94.11   $94.10   $94.10  
  Purchase #6 $127.82   6.360%   $135.9494   $135.95   $135.95   $135.90  
  Purchase #7 $22.99   6.767%   $24.5457   $24.55   $24.55   $24.50  
  7 purchase totals = $546.48       $583.4716   $583.47   $583.40   $583.50