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 $239.27   3.544%   $247.7497   $247.75   $247.75   $247.70  
  Purchase #2 $19.27   10.289%   $21.2527   $21.25   $21.25   $21.30  
  Purchase #3 $155.26   4.592%   $162.3895   $162.39   $162.40   $162.40  
  Purchase #4 $21.27   9.258%   $23.2392   $23.24   $23.25   $23.20  
  Purchase #5 $186.73   13.193%   $211.3653   $211.37   $211.35   $211.40  
  Purchase #6 $130.77   10.739%   $144.8134   $144.81   $144.80   $144.80  
  Purchase #7 $42.88   3.820%   $44.518   $44.52   $44.50   $44.50  
  7 purchase totals = $795.45       $855.3278   $855.33   $855.30   $855.30