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 $23.35   12.145%   $26.1859   $26.19   $26.20   $26.20  
  Purchase #2 $193.98   7.267%   $208.0765   $208.08   $208.10   $208.10  
  Purchase #3 $145.92   10.407%   $161.1059   $161.11   $161.10   $161.10  
  Purchase #4 $239.70   5.142%   $252.0254   $252.03   $252.05   $252.00  
  Purchase #5 $49.41   4.175%   $51.4729   $51.47   $51.45   $51.50  
  Purchase #6 $58.46   10.116%   $64.3738   $64.37   $64.35   $64.40  
  Purchase #7 $246.51   4.864%   $258.5002   $258.50   $258.50   $258.50  
  7 purchase totals = $957.33       $1,021.7406   $1,021.75   $1,021.75   $1,021.80