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 $59.38   11.705%   $66.3304   $66.33   $66.35   $66.30  
  Purchase #2 $136.37   6.488%   $145.2177   $145.22   $145.20   $145.20  
  Purchase #3 $46.65   13.769%   $53.0732   $53.07   $53.05   $53.10  
  Purchase #4 $119.90   13.372%   $135.933   $135.93   $135.95   $135.90  
  Purchase #5 $186.54   11.373%   $207.7552   $207.76   $207.75   $207.80  
  Purchase #6 $12.25   10.867%   $13.5812   $13.58   $13.60   $13.60  
  Purchase #7 $101.73   5.172%   $106.9915   $106.99   $107.00   $107.00  
  7 purchase totals = $662.82       $728.8822   $728.88   $728.90   $728.90