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 $182.69   13.223%   $206.8471   $206.85   $206.85   $206.80  
  Purchase #2 $233.43   8.181%   $252.5269   $252.53   $252.55   $252.50  
  Purchase #3 $41.69   12.777%   $47.0167   $47.02   $47.00   $47.00  
  Purchase #4 $242.71   13.417%   $275.2744   $275.27   $275.25   $275.30  
  Purchase #5 $19.64   3.270%   $20.2822   $20.28   $20.30   $20.30  
  Purchase #6 $107.55   13.501%   $122.0703   $122.07   $122.05   $122.10  
  Purchase #7 $86.94   3.768%   $90.2159   $90.22   $90.20   $90.20  
  7 purchase totals = $914.65       $1,014.2335   $1,014.24   $1,014.20   $1,014.20