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 $38.87   8.869%   $42.3174   $42.32   $42.30   $42.30  
  Purchase #2 $122.85   10.859%   $136.1903   $136.19   $136.20   $136.20  
  Purchase #3 $6.65   13.511%   $7.5485   $7.55   $7.55   $7.50  
  Purchase #4 $233.45   4.813%   $244.6859   $244.69   $244.70   $244.70  
  Purchase #5 $211.65   11.210%   $235.376   $235.38   $235.40   $235.40  
  Purchase #6 $94.51   3.861%   $98.159   $98.16   $98.15   $98.20  
  Purchase #7 $178.53   5.522%   $188.3884   $188.39   $188.40   $188.40  
  7 purchase totals = $886.51       $952.6655   $952.68   $952.70   $952.70