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 $24.91   3.730%   $25.8391   $25.84   $25.85   $25.80  
  Purchase #2 $50.76   10.393%   $56.0355   $56.04   $56.05   $56.00  
  Purchase #3 $250.27   13.442%   $283.9113   $283.91   $283.90   $283.90  
  Purchase #4 $147.66   9.831%   $162.1765   $162.18   $162.20   $162.20  
  Purchase #5 $49.49   12.248%   $55.5515   $55.55   $55.55   $55.60  
  Purchase #6 $145.72   6.363%   $154.9922   $154.99   $155.00   $155.00  
  Purchase #7 $194.26   12.345%   $218.2414   $218.24   $218.25   $218.20  
  7 purchase totals = $863.07       $956.7475   $956.75   $956.80   $956.70