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 $208.54   10.323%   $230.0676   $230.07   $230.05   $230.10  
  Purchase #2 $168.75   3.306%   $174.3289   $174.33   $174.35   $174.30  
  Purchase #3 $98.64   13.177%   $111.6378   $111.64   $111.65   $111.60  
  Purchase #4 $116.43   8.176%   $125.9493   $125.95   $125.95   $125.90  
  Purchase #5 $125.53   3.295%   $129.6662   $129.67   $129.65   $129.70  
  Purchase #6 $5.30   10.409%   $5.8517   $5.85   $5.85   $5.90  
  Purchase #7 $222.35   11.298%   $247.4711   $247.47   $247.45   $247.50  
  7 purchase totals = $945.54       $1,024.9726   $1,024.98   $1,024.95   $1,025.00