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 $226.59   6.602%   $241.5495   $241.55   $241.55   $241.50  
  Purchase #2 $92.90   10.639%   $102.7836   $102.78   $102.80   $102.80  
  Purchase #3 $35.50   10.685%   $39.2932   $39.29   $39.30   $39.30  
  Purchase #4 $29.78   9.246%   $32.5335   $32.53   $32.55   $32.50  
  Purchase #5 $58.70   11.489%   $65.444   $65.44   $65.45   $65.40  
  Purchase #6 $225.49   3.453%   $233.2762   $233.28   $233.30   $233.30  
  Purchase #7 $174.67   7.177%   $187.2061   $187.21   $187.20   $187.20  
  7 purchase totals = $843.63       $902.0861   $902.08   $902.15   $902.00