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 $57.96   10.466%   $64.0261   $64.03   $64.05   $64.00  
  Purchase #2 $235.59   7.649%   $253.6103   $253.61   $253.60   $253.60  
  Purchase #3 $9.57   6.424%   $10.1848   $10.18   $10.20   $10.20  
  Purchase #4 $81.75   10.397%   $90.2495   $90.25   $90.25   $90.20  
  Purchase #5 $147.52   11.306%   $164.1986   $164.20   $164.20   $164.20  
  Purchase #6 $81.88   5.323%   $86.2385   $86.24   $86.25   $86.20  
  Purchase #7 $248.32   8.293%   $268.9132   $268.91   $268.90   $268.90  
  7 purchase totals = $862.59       $937.4210   $937.42   $937.45   $937.30