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 $226.74   12.573%   $255.248   $255.25   $255.25   $255.20  
  Purchase #2 $77.76   4.574%   $81.3167   $81.32   $81.30   $81.30  
  Purchase #3 $162.39   9.595%   $177.9713   $177.97   $177.95   $178.00  
  Purchase #4 $143.45   8.149%   $155.1397   $155.14   $155.15   $155.10  
  Purchase #5 $156.38   7.539%   $168.1695   $168.17   $168.15   $168.20  
  Purchase #6 $245.37   7.318%   $263.3262   $263.33   $263.35   $263.30  
  Purchase #7 $153.65   5.113%   $161.5061   $161.51   $161.50   $161.50  
  7 purchase totals = $1,165.74       $1,262.6775   $1,262.69   $1,262.65   $1,262.60