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 $88.50   11.380%   $98.5713   $98.57   $98.55   $98.60  
  Purchase #2 $112.25   12.554%   $126.3419   $126.34   $126.35   $126.30  
  Purchase #3 $153.88   13.758%   $175.0508   $175.05   $175.05   $175.10  
  Purchase #4 $216.61   5.836%   $229.2514   $229.25   $229.25   $229.30  
  Purchase #5 $24.58   13.527%   $27.9049   $27.90   $27.90   $27.90  
  Purchase #6 $103.97   10.388%   $114.7704   $114.77   $114.75   $114.80  
  Purchase #7 $240.33   13.625%   $273.075   $273.08   $273.10   $273.10  
  7 purchase totals = $940.12       $1,044.9657   $1,044.96   $1,044.95   $1,045.10